UNIVERSITY  OF  CALIFORNIA 
AT  LOS  ANGELES 


A   STUDY  OF 
THE  ABSORPTION   SPECTRA 


OF 


SOLUTIONS  OF  CERTAIN  SALTS  OF  POTASSIUM,  COBALT,  NICKEL,  COPPER, 

CHROMIUM,  ERBIUM,  PRASEODYMIUM,  NEODYMIUM,  AND 

URANIUM  AS  AFFECTED  BY  CHEMICAL  AGENTS 

AND  BY  TEMPERATURE 


BY 
HAEEY  C.  JONES  AND  W.  W.  STBONG 


WASHINGTON,  D.  C. 

PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 
1910 


CABNEGEE  INSTITUTION  OF  WASHINGTON 
PUBLICATION  No.  130 


OF  J.  B.  LIPPINCOTT  COMPANY 
PHILADELPHIA 


A  STUDY  OF  THE  ABSORPTION  SPECTRA 

OF 

SOLUTIONS  OF   CERTAIN  SALTS  OF  POTASSIUM,  COBALT,  NICKEL,  COP- 
PER, CHROMIUM,  ERBIUM,  PRASEODYMIUM,  NEODYMIUM,  AND 
URANIUM  AS  AFFECTED  BY  CHEMICAL  AGENTS 
AND  BY  TEMPERATURE 


BY 
HAEBY  C.  JONES  AND  W.  W.  STBONG 


2091 60 


PREFACE. 

This  investigation  on  the  absorption  spectra  of  solutions  is  a  continua- 
tion of  the  work  of  Jones  and  Uhler  and  Jones  and  Anderson,  and  has  been 
made  possible  by  grants  generously  awarded  by  the  Carnegie  Institution 
of  Washington.  The  results  obtained  from  the  study  of  about  3000  solu- 
tions are  recorded  in  this  monograph.  These  include  salts  of  potassium 
with  a  colored  anion,  cobalt,  nickel,  copper,  chromium,  erbium,  praseo- 
dymium, neodymium,  and  uranyl  and  uranous  uranium. 

The  effect  of  the  addition  of  free  acids  and  foreign  salts  on  the  absorp- 
tion spectra  is  studied  at  some  length  and  in  considerable  detail,  and  results 
have  been  obtained  which  show  that  chemical  reactions  in  general  are 
probably  much  more  complex  than  is  represented  by  the  equations  which 
are  usually  employed  to  express  such  chemical  changes. 

The  effect  of  the  nature  of  the  solvents  on  the  absorption  spectra  of  sub- 
stances dissolved  in  those  solvents  has  been  one  of  the  chief  points  investi- 
gated in  this  work.  It  is  shown  that  solvents  which  themselves  do  not 
absorb  visible  light  may  have  a  determining  influence  on  the  absorption 
of  the  dissolved  substances.  Well-defined  "solvent-bands"  have  been  dis- 
covered for  water,  the  alcohols,  acetone,  and  glycerol.  These  bands  are 
perfectly  characteristic  of  each  solvent,  and  their  existence  is  regarded  as 
strong  evidence  for  the  theory  of  solvation,  upon  which  work  has  been  in 
progress  in  this  laboratory  for  the  past  12  years. 

It  is  difficult  to  see  how  the  solvent  can  affect  so  markedly  the  resonance 
of  the  vibrators  unless  it  forms  some  kind  of  a  compound  or  system  with 
the  dissolved  substance.  Indeed,  I  am  inclined  to  regard  this  evidence  from 
the  absorption  spectra  of  solutions,  for  the  general  correctness  of  the  solvate 
theory  of  solutions,  as  being  so  strong  and  unambiguous  that  there  scarcely 
remains  a  reasonable  doubt  that  dissolved  molecules  and  especially  ions 
combine  with  more  or  less  of  the  solvent.  This  is  especially  true  when  we 
take  into  account  the  various  other  lines  of  evidence,  all  of  which  point 
to  the  same  conclusion. 

A  large  amount  of  work  has  been  done  on  the  effect  of  temperature 
on  the  absorption  spectra  of  aqueous  solutions,  and  the  results  are  here 
recorded.  A  special  form  of  apparatus  was  designed  by  Dr.  Anderson  for 
this  work,  involving  the  principle  of  total  reflection  from  quartz  prisms, 
which  was  found  to  work  admirably.  These  prisms  being  movable  in  a 
glass  trough  containing  the  solutions,  allowed  different  lengths  of  the  solu- 
tions, and,  consequently,  very  different  concentrations,  to  be  interposed 
into  the  path  of  the  beam  of  light. 

A  piece  of  pressure  apparatus  with  thick  steel  walls  and  quartz  and  glass 
ends  has  been  devised  for  work  with  aqueous  and  nonaqueous  solutions 
at  high  temperatures,  and  we  are  now  studying  the  absorption  spectra 
of  such  solutions  at  high  temperatures. 


VI  PREFACE. 

A  form  of  apparatus  has  been  devised  which  enables  us  to  measure 
the  intensities  of  the  absorption  bands  in  aqueous  and  nonaqueous  solu- 
tions, over  a  range  of  temperature;  and  work  is  now  in  progress  on  this 
part  of  the  problem. 

As  soon  as  sufficient  work  has  been  done  on  inorganic  compounds  we 
intend  to  take  up  organic  substances  and  study  them  by  the  same  general 
methods  that  we  have  used  with  the  inorganic. 

For  the  conductivity  measurements  recorded  in  this  monograph  we 
are  indebted  to  Dr.  A.  P  West  and  Mr.  H.  H.  Hosford. 

It  gives  me  pleasure  to  express  my  thanks  to  Professor  Ames  for  the 
loan  of  the  grating  used  in  this  work,  and  for  the  ample  space  placed  at 
our  disposal  in  carrying  out  this  investigation. 

HARRY  C.  JONES. 


CONTENTS. 


CHAPTER  I.    INTRODUCTION 1 

Recent  Spectroscopic  Investigations 1 

Spectra  of  Gases 3 

Spectra  of  Liquids  and  Solids 6 

Banded  Spectra 7 

A  Method  of  Chemical  Analysis 8 

Atomic  Structure  and  Spectra 9 

Organic  Absorption  Spectra — The  Unit  of  this  Absorption 10 

The  Theory  of  Chromophores 11 

Theory  of  Dynamic  Isomerism 12 

Theory  of  Stark 13 

Complexity  of  the  Problem  of  the  Spectra  of  Compounds 13 

Method  of  Attacking  the  Problem  of  Emission  and  Absorption  Spectra 16 

CHAPTER  II.    EXPERIMENTAL  METHODS 19 

CHAPTER  III.      POTASSIUM  SALTS 23 

Potassium  Chromate 25 

Potassium  Dichromate 26 

Potassium  Ferrocyanide  in  Water 27 

Potassium  Ferricyanide  in  Water 28 

CHAPTER  IV.    COBALT  SALTS 31 

Review  of  Previous  Work 31 

Glycerol  Solutions  of  Cobalt  Salts 34 

Aqueous  Solutions  of  Cobalt  Salts 34 

Cobalt  Nitrate 37 

Cobalt  Sulphate 38 

Cobalt  Acetate 38 

Cobalt  Chloride  and  Calcium  Chloride 38 

Cobalt  Chloride  and  Aluminium  Chloride 39 

Cobalt  Sulphocyanate 40 

Cobalt  Chloride  in  Water,  Conductivity  and  Dissociation 41 

Cobalt  Bromide  in  Water,  Conductivity  and  Dissociation 41 

Cobalt  Nitrate  in  Water,  Conductivity  and  Dissociation 41 

Summary 42 

CHAPTER  V.    NICKEL  SALTS 43 

Introduction 43 

Nickel  Chloride 43 

Nickel  Sulphate 44 

Nickel  Acetate 44 

Nickel  Chloride  in  Water,  Conductivity  and  Dissociation 45 

Nickel  Nitrate  in  Water,  Conductivity  and  Dissociation 45 

CHAPTER  VI.    COPPER  SALTS 47 

Copper  Bromide 47 

Copper  Nitrate 47 

CHAPTER  VII.    CHROMIUM  SALTS 49 

Introduction 49 

Chromium  Chloride 51 

Chromium  Chloride  and  Aluminium  Chloride 52 

vii 


Viii  CONTENTS. 

CHAPTER  VII.     CHROMIUM  SALTS — continued. 

Chromium  Chloride  and  Calcium  Chloride 52 

Chromium  Nitrate 53 

Chromium  Sulphate 53 

Chromium  Acetate 54 

Chrome  Alum 54 

Chromium  Chloride  in  Water,  Conductivity  and  Temperature 55 

Chromium  Nitrate  in  Water,  Conductivity  and  Coefficients 55 

CHAPTER  VIII.    ERBIUM  SALTS 57 

Erbium  Chloride  in  Glycerol 63 

Erbium  Chloride  in  Water,  Effect  of  Temperature 63 

Absorption  Spectra  of  Erbium  Nitrate  and  other  Salts  of  Erbium 64 

CHAPTER  IX.    PRASEODYMIUM  SALTS 65 

Introduction 65 

Praseodymium  Chloride 65 

Praseodymium  Nitrate 66 

CHAPTER  X.    NEODYMIUM  SALTS 69 

Introduction 69 

The  Effect  of  Rise  in  Temperature  on  the  Absorption  Spectra  of  Aqueous  Solutions 

of  Neodymium  Salts 72 

Neodymium  Salts  in  Glycerol 78 

Neodymium  Nitrate  in  Nitric  Acid 79 

Spectrophotography  of  Chemical  Reactions 79 

Summary 83 

CHAPTER  XI.    URANIUM  SALTS 85 

The  Absorption  Spectra  of  Uranium  Compounds 85 

The  Absorption  Spectrum  of  Uranyl  Chloride 89 

Uranyl  Chloride  in  Aqueous  Solutions 89 

Uranyl,  Calcium,  Aluminium,  and  Zinc  Chlorides  in  Water 91 

Uranyl  Chloride  in  Methyl  Alcohol 93 

Uranyl  Chloride  and  Calcium  Chloride  in  Methyl  Alcohol 94 

Uranyl  Chloride  in  Methyl  Alcohol  and  Water 95 

Uranyl  Chloride  in  Ethyl  Alcohol 96 

Uranyl  Chloride  in  Glycerol 97 

Uranyl  Chloride  in  Mixtures  of  Glycerol  and  Methyl  Alcohol 97 

Uranyl  Chloride  in  Acetone  and  the  Effect  of  Hydrochloric  Acid  on  the  Uranyl 

Acetate  Bands 97 

Uranyl  Chloride  in  Acetone  and  Water 98 

Uranyl  Chloride,  Temperature  Effect 98 

Absorption  Spectrum  of  Anhydrous  Uranyl  Chloride 99 

Absorption  Spectrum  of  Uranyl  Nitrate  under  Different  Conditions 99 

Uranyl  Nitrate  in  Aqueous  Solution 99 

Absorption  Spectrum  of  Uranyl  Nitrate  Crystals 101 

Effect  of  Dilution  on  the  Uranyl  Bands 102 

Uranyl  Nitrate  in  Nitric  Acid 102 

Uranyl  Nitrate  in  Methyl  Alcohol 103 

Uranyl  Nitrate  in  Methyl  Alcohol  and  Water 103 

Uranyl  Nitrate  in  Ethyl  Alcohol 105 

Uranyl  Nitrate  in  Mixtures  of  Glycerol,  Water,  Acetone,  and  Ethyl  Alcohol.   106 

Uranyl  Nitrate,  Temperature  Effect 106 

Absorption  Spectrum  of  Anhydrous  Uranyl  Nitrate 107 

Uranyl  Bromide  in  Water 108 

Uranyl  Sulphate,  Temperature  Effect 108 

Uranyl  Sulphate  Mixed  with  Concentrated  Sulphuric  Acid 109 

Uranyl  Acetate  in  Water 110 

Anhydrous  Uranyl  Acetate Ill 

Uranyl  Acetate  in  Methyl  Alcohol Ill 


CONTENTS.  IX 

CHAPTER  XI.    URANIUM  SALTS — continued. 

The  Uranyl  Bands  of  the  Acetate 112 

Uranyl  Acetate,  Temperature  Effect 112 

Spectrophotography  of  Chemical  Reactions  of  Uranyl  Salts 112 

Uranyl  Chloride  in  Water,  Conductivity  and  Temperature  Coefficients 115 

Uranyl  Nitrate  in  Water,  Conductivity  and  Temperature  Coefficients 115 

Uranyl  Sulphate  in  Water,  Conductivity  and  Temperature  Coefficients 115 

Uranyl  Acetate  in  Water,  Conductivity  and  Temperature  Coefficients 116 

The  Phosphorescent  and  Fluorescent  Spectra  of  Uranyl  Salts 116 

Uranous  Salts 121 

Uranous  Chloride  in  Water 122 

Uranous  and  Aluminium  Chlorides  in  Water 123 

Uranous  Chloride  in  Hydrochloric  Acid  and  Acetone 124 

Uranous  Chloride  in  Mixtures  of  Methyl  Alcohol  and  Water,  and  of  Methyl 

Alcohol  and  Acetone 124 

Uranous  Chloride  in  Water  and  Ethyl  Alcohol 125 

Uranous  Chloride  in  Acetone  and  Water 125 

Uranous  Chloride  in  Methyl  and  Ethyl  Alcohols 125 

Uranous  Chloride  in  Glycerol 126 

Uranous  Chloride  in  Mixtures  of  Glycerol  and  Water 126 

Uranous  Chloride  in  Mixtures  of  Glycerol  and  Methyl  Alcohol,  Glycerol  and 

Ethyl  Alcohol,  and  Glycerol  and  Acetone 127 

Uranous  Chloride  in  Acetone,  in  Methyl  Alcohol,  and  in  Glycerol 127 

Uranous  Chloride  in  Methyl  Alcohol  and  Ether 128 

Effect  of  the  Presence  of  Acids  on  the  Uranous  Bands 128 

Uranous  Chloride  in  Water  and  Methyl  Alcohol,  Water  and  Acetic  Acid, 

Water  and  Nitric  Acid,  Water  and  Sulphuric  Acid 129 

Uranous  Chloride  to  Which  Acetic  Acid  is  Added 130 

Uranous  Bromide 130 

Uranyl  and  Uranous  Acetates 130 

Absorption  Spectrum  of  Dry  Uranous  Acetate 131 

Uranous  Acetate  in  Methyl  Alcohol  and  Acetic  Acid 131 

Uranous  Acetate  in  Glycerol 132 

Effect  of  Temperature  on  the  Absorption  Spectra  of  Uranous  Chloride 132 

The  Wave-lengths  of  the  Uranous  and  Uranyl  Bands  under  Varying  Conditions  133 

Alcohol  Solutions  of  Uranium  Salts 133 

Glycerol  Solutions 134 

Uranyl  Salts  in  the  Presence  of  Free  Acid 134 

Effect  of  the  Presence  of  Foreign  Salts 134 

Effect  of  Free  Acid 135 

CHAPTER  XII.    GENERAL  DISCUSSION  OF  RESULTS 137 

Bearing  of  the  Solvate  Theory  of  Solution 142 

BIBLIOGRAPHY,  PAPERS,  MONOGRAPHS 145 

DESCRIPTION  OF  THE  PLATES 147 


CHAPTER  I. 

INTRODUCTION. 

Recent  Spectroscopic  Investigations.  —  Spectra  of  Gases,  Spectra  of  Liquids  and 
Solids,  banded  Spectra.  —  A  Method  of  Chemical  Analysis.  —  Atomic  Structure 
and  Spectra.  —  Organic  Absorption  Spectra,  including  Unit  of  Absorption,  The- 
ory of  Chromophores,  Theory  of  Dynamic  Isomerism,  and  Stark's  Theory.  —  The 
Complexity  of  Spectra.  —  Method  of  Attacking  the  Problem  of  Emission  and 
Absorption  Spectra. 

The  study  of  the  various  phenomena  of  light  may  be  divided  into 
three  parts:  The  emission  of  light  by  matter,  the  transmission  of  light 
through  space,  and  the  absorption  of  light  by  matter.  The  theory  of  the 
transmission  of  light  as  an  electromagnetic  phenomenon  was  first  proposed 
by  Faraday  and  Maxwell.  On  this  theory  it  is  assumed  that  in  all  regions 
of  space  through  which  light  passes  there  are  electric  and  magnetic  fields. 
In  an  electric  field  there  exists  a  certain  state  of  things  that  gives  rise  to  a 
force  acting  on  any  electric  charge  that  may  exist  there.  This  is  the  electric 
force  and  this  represents  the  state  of  the  region  of  space  considered.  In  a 
similar  way  the  magnetic  field  is  also  defined.  A  relation  is  then  found 
between  the  electromagnetic  quantities  which  is  usually  called  Maxwell's 
equations,  or  is  a  modified  form  of  these  equations.  Starting  with  these 
equations,  Maxwell  showed  that  the  state  of  things  represented  by  his 
fundamental  equations  consists  of  the  propagation  of  a  periodic  variation 
of  the  electric  and  magnetic  forces  through  space  with  the  velocity  of  light. 
So  well  does  the  nature  of  these  electromagnetic  waves  agree  with  the  prop- 
erties of  light  as  transmitted  by  the  ether  and  transparent  bodies  that  light 
is  at  present  considered  to  be  an  electromagnetic  disturbance  itself.  The 
simplest  case  of  light-waves  is  that  of  plane  polarized  waves  traveling  in 
the  direction  of  the  x  axis.  Waves  of  this  kind  are: 


n(t  --  J  Hg  =  aco3n(t  --  j 


v  =  a  cos 

Ey,  the  component  of  the  electric  force  in  the  y  direction,  is  the  only  com- 
ponent of  the  electric  force  that  has  a  value.  The  magnetic  force  has  a 
component  only  in  the  z  direction,  Hz.  a  is  the  amplitude  of  the  disturb- 
ance, t  is  the  time,  n  is  the  number  of  vibrations  in  a  time  2it  and  c  is  the 
velocity  of  light. 

RECENT   SPECTROSCOPIC  INVESTIGATIONS. 

A  light-wave  in  the  "ether"  is  an  electromagnetic  disturbance  that  is 
propagated  in  free  space  without  any  distortion  of  form  or  any  dissipation 
of  energy,  one  of  the  properties  of  electric  and  magnetic  fields  being  the 
power  to  store  energy.  When  a  light-wave  strikes  ordinary  matter  it  is  in 
general  broken  up  into  several  parts.  If  the  surface  of  the  body  is  smooth, 
a  considerable  part  of  the  energy  will  be  taken  up  by  a  regularly  reflected 

1 


2  A  STUDY  OF  THE  ABSORPTION  SPECTRA. 

wave.  If  the  surface  is  rough,  a  great  number  of  so-called  waves  will  be 
reflected.  The  remaining  part  of  the  disturbance  will  advance  through 
the  body.  As  no  body  is  a  perfect  reflector  or  absolutely  transparent,  it 
follows  that  part  of  the  energy  of  the  light-wave  remains  with  the  body. 
This  phenomenon  is  known  as  the  absorption  of  light.  We  also  know  of 
many  conditions  of  matter  in  which  light  is  emitted.  The  object  of  the 
study  of  emission  and  absorption  of  light  is  to  gain  some  knowledge  of  the 
mechanism  of  matter  by  which  it  is  enabled  to  produce  or  absorb  electro- 
magnetic waves.  The  expression  of  the  properties  of  different  kinds  of 
matter  by  different  values  of  the  dielectric  constant  («),  the  conductivity 
(<r)  or  the  magnetic  permeability  (fi)  has  not  been  found  to  be  satisfactory. 

The  electromagnetic  mechanism  which  at  present  is  considered  as  the 
basis  of  the  theories  of  radiation  and  absorption  is  the  electron.  The 
charge  which  it  carries  has  been  found  to  be  the  atomic  unit  of  electricity. 
Experimental  results  in  electricity  can  be  explained  on  this  basis.  The 
electron  is  found  in  the  vacuum  discharge-tube,  in  the  radiations  from 
radioactive  matter,  in  arcs,  in  sparks,  in  secondary  radiations.  They  are 
present  in  all  bodies.  By  the  distribution  and  motions  of  these  electrons  men 
of  science  to-day  attempt  to  explain  all  electrical  and  optical  phenomena. 
Some  electrons  in  a  conducting  body  are  in  a  free  state,  so  that  they  can 
obey  an  electric  force.  Richardson  and  Brown1  have  shown  that  ions 
emitted  by  hot  platinum  (and  approximately  so  for  other  metals)  are 
kinetically  identical  with  the  molecules  of  a  gas,  of  equal  molecular  weight, 
at  the  temperature  of  the  metal.  This  holds  for  the  mode  of  distribution 
of  velocity  as  well  as  its  average  value,  and  shows  that  the  free  electrons 
inside  the  metal  have  the  same  amount  and  mode  of  distribution  of  velocity 
and  kinetic  energy  as  the  molecules  of  a  gas  of  equal  molecular  weight  at 
the  temperature  of  the  metal. 

In  the  case  of  a  nonconducting  substance  the  electrons  are  considered 
as  bound  to  certain  positions  of  equilibrium.  In  a  conductor  in  an  electric 
field  there  is  an  excess  of  electrons  at  one  end.  In  a  dielectric,  as  soon  as 
an  electron  is  displaced  from  a  position  of  equilibrium,  a  new  (elastic) 
force  is  brought  into  play  which  pulls  the  electron  back  to  its  original  posi- 
tion. The  motion  of  electrons  in  nonconducting  bodies,  together  with  the 
change  of  dielectric  displacement  of  the  ether  itself,  makes  up  Maxwell's 
displacement-current.  Under  the  influence  of  the  elastic  forces  the  elec- 
trons can  vibrate  about  their  positions  of  equilibrium  and  may  thus  become 
the  centers  of  electromagnetic  waves.  In  this  way  may  be  explained  the 
emission  of  light  and  heat.  Absorption  results  when  the  electrons  are  set 
into  vibration  by  a  beam  of  light,  and  part  of  the  vibrating  energy  of  the 
electron  is  transformed  into  heat  energy. 

As  to  the  nature  of  the  electron  very  little  is  known.  On  the  other 
hand,  the  mathematical  electron  is  much  better  known.  As  the  recent 
experiments  by  Bucherer2  on  the  value  of  c/m  agree  with  values  calculated 
by  Lorentz,  use  will  be  made  here  of  his  conception  of  the  electron.  To 
each  electron  is  ascribed  certain  definite  dimensions.  The  ether  is  assumed 

1  PhU.  Mag.,  16,  353  and  740  (1908).  »  Phys.  Zeit.,  9,  755  (1908). 


INTRODUCTION.  3 

to  pervade  not  only  the  space  between  atoms  but  also  the  space  within 
atoms  and  electrons;  and  is  also  assumed  to  be  at  rest.  There  will  be  an 
electromagnetic  field  within  the  electron  as  well  as  without.  Various  dis- 
tributions of  charge  may  be  assumed.  Lorentz  usually  assumes  a  volume 
density  (p)  distribution  such  that  p  is  a  continuous  function  of  the  coordi- 
nates. The  charged  particle  has  then  no  sharp  boundary,  but  is  surrounded 
by  a  thin  layer  in  which  the  density  gradually  sinks  from  p  to  0.  The  ether 
is  simply  the  space  in  which  a  certain  state  of  the  electromagnetic  field 
exists.  (Recently  very  interesting  papers  by  Einstein  and  others  on  this 
subject  have  appeared.)  The  electron  having  been  thus  defined,  equations 
can  be  formed  for  the  electric  and  magnetic  fields  for  any  region  in  which 
there  are  electrons  either  at  rest  or  in  motion. 

Having  considered  the  elementary  unit  of  the  mechanism  of  optical 
phenomena,  let  us  now  turn  to  some  of  the  phenomena  themselves. 

(a)    SPECTRA   OP    GASES. 

For  optical  purposes  bodies  may  be  divided  into  gases  and  into  solids 
and  liquids.  The  spectra  of  gases  consist  of  an  enormous  number  of  fine 
lines  and  are  usually  grouped  into  line  and  band  spectra.  Band-spectra 
themselves  consist  of  a  great  number  of  sharp  lines  spaced  in  a  very  regular 
manner,  whereas  line-spectra  consist  of  lines  apparently  spaced  more  or 
less  at  random  in  the  spectrum,  although  some  of  the  lines  have  been  found 
to  have  frequencies  that  are  connected  by  certain  series  relations.  Good 
examples  of  band-spectra  are  the  absorption  spectra  of  fluorine,  bromine, 
iodine,  chlorine,  sulphur,  or  sodium  vapors.  These  consist  of  thousands 
of  very  fine  lines.  Very  interesting  work  has  recently  been  done  by  Wood 
on  the  magnetic-rotation  spectrum  and  the  fluorescent  spectrum  of  sodium 
vapor.  On  exciting  fluorescence  by  monochromatic  light  of  different  wave- 
lengths it  is  possible  to  set  into  vibration  apparently  different  systems  in 
the  sodium  atoms  or  clusters  containing  sodium  atoms,  each  one  of  these 
systems  of  vibrators  emitting  a  different  series  of  bands.  It  is  found  that 
the  presence  of  foreign  gases  has  a  very  great  effect  upon  the  absorption 
spectra  of  sodium.  The  presence  of  hydrogen  prevents  fluorescence. 
Wood  1  found  that  as  mercury-vapor  is  evolved  in  a  vacuum  the  band 
X  2536  broadens  rapidly  on  the  less  refrangible  side,  attaining  a  width  of  300 
or  400  Angstrom  units.  There  is  a  little  broadening  in  the  other  direction. 
If  hydrogen  or  some  other  inert  gas  is  present,  the  band  broadens  symmetri- 
cally at  first.  Larmor2  has  suggested  that  this  unsymmetrical  widening  may 
be  due  to  the  formation  of  loose  molecular  aggregates,  which  vibrate  in  longer 
periods  owing  to  this  mutual  influence.  Wood  and  Guthrie 3  find  that  the 
cadmium  absorption  band  X  2288  broadens  symmetrically  in  the  case  of 
pure  cadmium  but  very  asymmetrically  when  mercury  is  present.  A  very 
promising  field  for  research  is  suggested  by  this  work,  one  that  will  probably 
throw  much  light  upon  the  mechanism  within  the  atoms  themselves. 

Quite  recently  Dufour  4  has  succeeded  in  obtaining  the  Zeeman  phe- 

1  Astrophys.  Journ.,  26,  41  (1907).  8  Ibid.,  28,  211  (1909). 

1  Ibid.,  26,  120  (1907).  «  Phys.  Zeit.,  4,  124  (1909). 


4  A   STUDY   OP   THE    ABSORPTION   SPECTRA. 

nomena  for  many  of  the  bands  of  the  emission  spectra  of  fluorides  and 
chlorides  of  calcium,  strontium,  barium,  and  silicon.  These  give  in  some 
cases  a  normal  and  in  other  cases  an  abnormal  longitudinal  Zeeman  (light 
being  parallel  to  the  magnetic  field)  doublet,  the  normal  doublet  usually 
being  considered  as  originating  from  a  negative  charge  and  an  abnormal 
doublet  as  due  to  a  positive  charge.  The  only  difference  in  these  two 
effects  is  that  the  light  is  circularly  polarized  in  opposite  directions  for 
corresponding  components  of  the  doublet.  Dufour  considers  that  so  far 
all  spectra  (emission  or  absorption)  that  show  the  abnormal  Zeeman  effect 
have  their  centers  in  the  molecules.  If  one  considers  the  explanation  to 
be  due  to  positive  and  negative  electrons,  then  the  value  of  elm  for  these 
will  be  about  the  same  except  in  the  case  of  some  of  the  bands  of  xenotine. 
At  the  University  of  Manchester  it  has  been  shown  that  the  Humphrey- 
Mohler  pressure-shift  is  to  be  observed  for  bands  that  give  the  Zeeman 
effect.  With  the  exception  of  the  few  bands  described  by  Dufour,  the 
wave-length  of  bands  is  unalterable  by  physical  and  chemical  changes. 

The  band-spectra  are  very  complex  indeed.  In  Watts's  "Index  to 
Spectra"  the  wave-lengths  of  over  5,000  bands  are  given  for  sulphur  between 
>l  6400  and  vl  3600,  over  2,700  lines  for  iodine  between  >l  6300  and  yl  5100, 
over  2,800  for  bromine  between  >l  6200  and  A  5100,  and  over  2,600  for  alumi- 
nium oxide  between  X  5200  and  X  4400.  Complex  as  these  spectra  are,  the 
so-called  line-spectra  of  the  elements  are  even  more  complex.  The  same 
author  gives  the  wave-lengths  of  over  2,300  lines  for  chromium,  3,000  for 
iridium,  2,300  for  iron  (spark),  3,000  for  tungsten  (spark),  and  5,200  for 
uranium  (spark).  For  most  of  these  elements  the  greatest  number  of  lines 
lie  in  the  regions  of  shorter  wave-lengths,  and  in  most  cases  the  maximum 
number  of  lines  lie  between  A  4000  and  A  3000.  For  example,  Watts  gives 
1,100  iron  lines  between  A  2000  and  3000,  over  1,400  lines  between  I  3000 
and  4000,  1,100  lines  between  >l  4000  and  5000,  over  600  lines  between  A  5000 
and  6000,  and  only  a  little  over  300  between  A  6000  and  6750.  A  similar 
distribution  holds  for  vanadium,  osmium,  etc.  The  work  of  Schumann 
and  Lyman  shows  that  many  more  lines  exist  in  the  ultra-violet  down  to 
Jl  1000,  but  it  seems  quite  probable  that  most  of  the  spark  and  arc  lines  lie 
either  in  the  visible  or  in  the  adjacent  ultra-violet  regions  of  the  spectrum. 

When  the  source  of  the  line-spectrum  is  subjected  to  physical  changes 
the  width  and  relative  intensities  of  the  bands  change  enormously.  Ray- 
leigh  *  and  Michelson  2  have  shown  that  the  Doppler  effect  accounts  for 
the  width  of  the  lines  when  the  pressure  is  small.  Michelson  gives  a  formula 
for  the  breadth  (6)  of  the  spectrum  lines, 


where  6  is  the  absolute  temperature,  m  the  molecular  weight,  a  and  d 
constants. 

At  present  only  two  physical  causes  are  known  to  change  the  frequency 
of  vibration  of  the  emitters  or  absorbers  of  the  line-spectrum.  One  of  these 
is  the  Humphrey-Mohler  effect — that  an  increase  of  pressure  about  the  source 

1  PhU.  Mag.,  27,  298  (1889).  2  Ibid.,  34,  280  (1892). 


INTRODUCTION.  5 

of  light  causes  the  lines  to  be  slightly  shifted  towards  the  red.  Humphreys 
considers  this  to  be  due  to  the  magnetic  fields  of  neighboring  atoms.  Rich- 
ardson,1 on  the  other  hand,  considers  the  shift  as  due  to  electrostatic  action. 
An  increase  of  the  partial  pressure  of  the  vapor  of  the  emitting  substance 
only  causes  the  lines  to  widen.  An  increase  of  the  total  pressure  of  the 
surrounding  vapor  causes  a  shift,  and  this  Richardson  considers  to  be  due 
to  sympathetic  vibrations  set  up  in  the  surrounding  atoms.  If  an  atom 
is  emitting  light,  it  must  be  surrounded  by  an  alternating  field  of  force, 
and  this  will  produce  forced  vibrations  of  equal  period  and,  under  certain 
conditions,  of  equal  phase  in  the  neighboring  atoms.  These  sympathetic 
vibrations  will  then  react  upon  the  emitting  atom  and  increase  its  period. 
After  making  several  assumptions  as  to  the  vibrator  in  the  emitting  atom, 
Richardson  deduces  a  shift  which  is  considerably  larger  than  that  observed. 

The  second  phenomenon  of  the  change  of  frequency  of  line-spectra  is 
that  of  the  Zeeman  effect.  Many  lines  show  a  simple  Zeeman  effect  such 
as  would  be  produced  upon  a  vibrating  negative  electron.  Other  lines  show 
a  very  complex  Zeeman  effect  which  as  yet  has  not  been  fully  explained. 
Still  other  lines  show  no  Zeeman  effect  at  all.  All  line-spectra  show  a 
Zeeman  effect  that  indicates  that  the  vibrator  carries  a  negative  charge. 
Series  lines  usually  show  a  similar  resolution  in  a  magnetic  field  as  well  as 
a  similar  behavior  under  variations  of  pressure,  temperature,  etc.  Very 
important  discussions  of  the  Zeeman  effect  by  Lorentz,  Voigt,  Ritz,  etc., 
have  recently  appeared. 

Some  interesting  work  has  recently  been  done  by  Lenard,2  Stark,8  and 
some  others  on  the  carriers  of  matter  that  are  emitting  light.  In  vacuum- 
tubes,  in  arcs,  in  flames,  and  in  the  radiations  from  radioactive  bodies  we 
have  electrons,  atoms,  molecules,  charged  atoms  or  molecules,  or  aggrega- 
tions of  these  that  are  moving  in  some  cases  with  very  great  velocities.  The 
free  electron,  as  we  shall  see,  radiates  a  continuous  spectrum,  but  the  bound 
electron,  being  disturbed  comparatively  infrequently  by  collisions  of  the 
atom  in  which  it  is  bound,  will  emit  more  or  less  monochromatic  radiations. 
Now,  in  the  case  of  flames,  arcs,  etc.,  it  is  possible  to  separate  the  positively 
and  negatively  charged  ions  by  means  of  an  electric  field. 

Lenard's  work  indicated  that  the  radiators  of  line-spectra  were  either 
neutral  atoms  of  positive  ions,  the  principal  series  being  due  to  neutral 
atoms,  and  the  subordinate  series  to  positively  charged  atoms.  If  an  ion 
has  a  swarm  of  molecules  about  it,  it  is  unable  to  radiate  or  absorb.  Stark 
studied  the  Doppler  effect  of  canal-rays  in  vacuum-tubes.  He  found  that 
in  the  case  of  a  beam  of  light  coming  from  the  canal-rays  in  the  same  direc- 
tion in  which  they  are  moving,  many  spectrum  lines  showed  a  "rest"  line 
and  a  displaced  line  due  to  the  Doppler  effect.  He  found  that  some  series 
lines  consisting  of  doublets  originate  from  univalent  positive  ions  and  the 
mercury  triplets  start  from  divalent  positive  ions.  Some  lines  show  no 
Doppler  effect  and  these  originate  from  a  negative  electron  joining  a  positive 
ion.  The  displaced  line  is  separated  from  the  normal  line  by  a  dark  space 

1  Phil.  Mag.,  14,  557  (1907). 

1  Ann.  Phys.,  9,  642  (1902);   1 1,  649  (1903);  12,  475,  737  (1903). 

1  Ibid.,  14,  506  (1904). 


6  A   STUDY   OF   THE    ABSORPTION  SPECTRA. 

which  is  found  to  be  wider  the  smaller  the  wave-length  of  the  line.  Assum- 
ing that  there  are  particles  of  varying  velocities  in  the  canal-rays,  Stark 
concludes  that  a  certain  velocity  is  necessary  before  a  particle  begins  to 
radiate  light  appreciably.  Stark  thus  considers  velocity  of  translation  as 
one  cause  of  radiation.  The  other  cause  of  continuous  radiation  of  energy 
by  an  atom  is  frequent  collision  with  electrons  or  other  charged  atoms. 

So  far  no  satisfactory  model  has  been  devised  that  will  act  as  a  source 
of  spectrum  lines.  No  system  that  includes  electrical  charges  in  orbital 
motion  is  permanent  on  account  of  their  radiation  of  energy.  The  favorite 
and  best  model  consists  of  systems  of  coaxial  circular  rings  of  equidistant 
electrons,  but  even  in  this  case  Schott l  has  shown  that  such  a  model  (in 
particular  that  of  Nagaoka),  although  giving  a  large  number  of  spectrum 
lines,  is  too  unstable  to  produce  wave-trains  of  sufficient  length. 

Stark  has  recently  suggested  the  possibility  of  explaining  a  positive 
charge  as  due  to  negative  electrons  revolving  in  circular  orbits,  the  centers 
of  these  circular  orbits  being  themselves  on  a  circle.  By  means  of  such  a 
device  a  positive  charge  can  easily  be  explained.  He  thinks  that  line- 
spectra  originate  from  a  system  of  this  kind.  The  general  trend  *  of  opinion 
seems  to  favor  the  view  that  spectrum  lines  are  due  to  some  special  mechan- 
isms in  the  atom  which  are  set  in  operation  during  ionization  and  operate 
for  only  a  short  time.  At  any  one  time  the  atom  may  be  radiating  light 
of  but  one  frequency. 

(6)    SPECTRA    OF    LIQUIDS    AND    SOLIDS. 

The  optical  phenomena  of  gases  are  so  much  better  understood  on 
account  of  our  more  perfect  knowledge  of  gases  that  considerable  space  has 
been  given  to  their  discussion.  On  the  other  hand,  the  conditions  in  liquids 
and  solids  are  so  exceedingly  complex  that  at  present  our  theories  are  in 
the  main  very  crude.  Considerable  advances  in  our  experimental  knowl- 
edge of  these  phenomena  have  recently  been  made  and  a  short  summary 
of  these  will  be  given. 

The  spectra  of  liquids  and  solids  can  be  roughly  divided  into  the  con- 
tinuous spectra  emitted  by  very  hot  liquids  or  solids,  secondary  X-ray 
radiations,  phosphorescent  or  fluorescent  spectra,  and  the  absorption  or 
emission  of  a  banded  spectra. 

According  to  the  present  theory,  X-rays,  and  possibly  /--rays,  and  the 
continuous  spectra  from  hot  liquids  and  solids  are  due  to  a  rapid  and  irregu- 
lar succession  of  sharp  electromagnetic  pulses,  each  of  which  is  due  to  the 
change  of  velocity  of  electrons.  Recent  work  on  X-  and  f-rays  indicates 
that  in  most  bodies  a  certain  homogeneous  secondary  radiation  is  excited 
when  the  body  is  exposed  to  the  X-  and  ?--rays.  This  secondary  radiation 
seems  very  similar  to  the  phosphorescent  bands  of  the  compounds  investi- 
gated by  Lenard  and  Klatt3  and  others.  Lenard  and  Klatt8  consider  that 
electrons  can  exist  in  three  different  states — in  a  "free"  state,  as  in  the  metals 

»  Phil.  Mag.,  15,  438  (1908). 

•  J.  J.  Thomson:  "The Corpuscular  Theory  of  Matter"  (1907).    Ladenburg  and  Loria: 

Nature,  79,  7  (1908).     Eagle:  Ibid.,  79,  68  (1908). 
•Ann.  Phys.,  15,  451  (1904). 


INTRODUCTION.  7 

where  they  take  part  in  conduction;  a  "liquid"  state  where  there  is  a  state 
of  motion  sensitive  to  light  vibrations;  and  a  "solid"  state  where  the  elec- 
trons take  part  in  neither  conduction  nor  the  absorption  of  light.  They 
consider  that  in  the  states  of  aggregation  which  cause  phosphorescent  bands 
there  are  certain  places  in  the  atoms,  dynamids,  where  electrons  can  be 
stored  at  low  temperatures.  To  each  phosphorescent  band  there  correspond 
then  these  phases:  (1)  an  upper  momentary  or  heat  phase;  (2)  a  perma- 
nent phase;  and  (3)  a  lower  momentary  phase.  For  a  great  many  bands 
they  succeed  in  obtaining  these  three  phases  when  they  change  the  tempera- 
ture sufficiently.  The  temperature  of  solid  hydrogen  is  sufficiently  low  to 
bring  most  of  the  phosphorescent  bands  into  the  lower  momentary  phase. 
In  this  phase  the  electrons  ejected  from  the  metallic  atom  by  photoelectric 
influence  of  illumination  are  fixed  and  stored  in  the  neighborhood,  only  a 
few  returning  immediately,  and  these  produce  the  "momentary  light" 
observed  during  illumination.  In  the  permanent  phase  the  electrons  are 
stored  for  a  certain  time  in  the  dynamids  and  eventually  return  to  the 
metallic  atom. 

Various  theories  have  been  proposed  to  explain  the  more  or  less  general 
absorption  throughout  large  regions  of  the  spectrum.  Drude  *  considers 
that  in  general  ultra-violet  bands  are  due  to  the  absorption  of  electrons, 
and  infra-red  bands  to  the  absorption  of  ions.  Houstoun,2  Pfund,*  and 
others  support  this  view. 

(c)    BANDED   SPECTRA. 

By  banded  spectra  we  shall  in  general  designate  bands  which  at  low 
temperatures  become  quite  fine,  such  as  the  uranyl,  neodymium,  or  erbium 
bands.  As  the  present  paper  deals  with  only  a  small  range  of  temperature 
and  concentration  and  but  one  solvent,  a  full  review  of  previous  work  will 
not  yet  be  given.  Rudorf  and  Washburn  have  given  a  very  good  review 
of  this  subject  from  the  hydrate  point  of  view. 

Brewster  observed,  in  1831,  that  the  transparency  and  color  of  many 
solids  change  when  they  are  heated.  Schonbein,  in  1852,  states  that  many 
bodies  become  more  highly  colored  at  higher  temperatures  while  at  low 
temperatures  they  lose  their  color.  He  found  that  sulphur  is  colorless  at 
—50°  C.  and  bromine  at  -70°  C.  Moissan  and  Dewar,  in  1903,  found  that 
fluorine  becomes  colorless  at  —253°,  so  that  at  low  temperatures  chlorine, 
bromine,  iodine,  and  fluorine  are  colorless. 

Conroy  (1891)  found  that  the  bands  of  cobalt  glass  are  displaced 
towards  the  red  with  rise  in  temperature.  Rizzo  (1891)  found  similar 
results  with  glasses  containing  cobalt,  didymium,  and  manganese.  Konigs- 
berger  (1901)  found  the  curve  of  absorption  to  be  displaced  towards  the  red 
with  rise  in  temperature,  but  concluded  that  the  maximum  of  absorption 
was  not  changed.  This  applied  to  the  wider  bands.  The  fine  bands  showed 
no  displacement  between  10°  and  500°  C.  Hartley  investigated  the  absorp- 
tion spectra  of  a  large  number  of  solutions  between  0°  and  100°.  He  inter- 

1  Ann.  Phys.,  14,  677-725,  936-961  (1904). 

1  Proc.  Roy.  Soc.,  606  (1909). 

1  Astrophys.  Journ.,  24,  19  (1906). 


A    STUDY    OF   THE    ABSORPTION  SPECTRA. 


preted  his  results  from  the  point  of  view  of  hydration.  Houstoun  investi- 
gated the  bands  of  glasses  containing  uranium  and  neodymium  but  found 
no  shifts  of  the  bands. 

Very  important  papers  on  this  subject  have  been  published  by  Becque- 
rel,  Ritz,  Retschinsky,  Stark,  Bois  and  Elias,  Konigsberger  and  Kilchling, 
Page,  Laub,  Voigt,  and  others. 

A  METHOD  OF  CHEMICAL  ANALYSIS. 

The  stimulus  to  research  along  many  lines  in  science  is  often  very  much 
augmented  by  the  requirements  of  technology.  This  is  especially  true  in 
connection  with  many  branches  of  organic  chemistry.  A  good  example  is 
the  case  of  the  pure  food  laws.  In  regulating  the  use  of  various  coloring  and 
preserving  matters  added  to  foods,  it  is  necessary  that  the  examiners  shall 
be  able  to  recognize  various  compounds  easily  and  quickly.  Many  organic 
compounds  possess  very  characteristic  colors,  and  it  has  often  been  asked 
whether  the  absorption  spectra  of  these  compounds  would  aid  in  their 
detection.  Our  present  knowledge  of  absorption  spectra  is  limited  chiefly 
to  the  visible  region  of  the  spectrum.  Before  this  method  of  analysis  can 
be  satisfactorily  used  by  chemists  it  will  be  necessary  to  measure  the  absorp- 
tion throughout  the  region  of  the  infra-red.  At  present  a  few  potassium 
salts  have  been  studied  in  the  regions  of  wave-lengths  as  long  as  0.1  mm. 
(The  shortest  electromagnetic  waves  that  are  produced  by  mechanical 
apparatus  are  about  6  mm.  in  length.) 

The  analysis  of  inorganic  compounds  by  means  of  their  spectra  is 
probably  less  hopeful,  although  the  absorption  or  reflection  spectra  would 
often  be  very  useful.  A  great  many  of  the  inorganic  cations  show  charac- 
teristic absorption  in  the  visible  portion  of  the  spectrum,  and  practically 
all  have  bands  in  the  infra-red.  J.  Formanek  *  has  suggested  that  the  absorp- 
tion spectra  of  metallic  compounds  of  alkannin  would  serve  to  indicate 
the  presence  of  the  metals. 

The  following  measurements  of  the  absorption  bands  of  different  com- 
pounds of  alkannin  show  the  effect  of  the  metal  upon  the  position  of  the  bands. 


Uranium 

J 

6870 

1 

6315 

A 
6210 

A 
5745    5340 

Iron 

6545 

6030 

Nickel 

6192 

5725    5320 

Potassium  
Cobalt 

6387 
6370 

5910 
5845    5405 

Calcium  

6147 
5953 

5682    5276 
5515    5128 

Sodium  

6337 

5857 

YyHFf  ;  
Aluminium  

5857 

5425    5048 

Barium  

6281 

5805    5395 

The  use  of  absorption  and  emission  spectra  has  been  most  successful 
in  separating  the  rare  earths.  The  method  has  been  used  by  Crookes, 
Becquerel,  Exner,  Demargay,  and  many  others.  A  very  good  account  of 
this  work  has  been  given  by  Bohm.2  Recently  Urbain  *  has  used  the  phos- 
phorescent spectra  to  purify  compounds  of  europium,  gadolinium,  terbium, 
dysprosium,  neoytterbium,  and  lutecium. 

1  Die  Qualitative  Spectralanalyse  anorganischer  Korper. 

2  Die  Daretellung  der  seltenen  Erden,  Leipzig  (1905). 
1  Le  Radium,  June  (1909). 


INTRODUCTION.  9 

ATOMIC   STRUCTURE    AND   SPECTRA. 

The  greatest  interest,  however,  lies  in  the  relation  between  chemical 
constitution  and  absorption  or  emission  spectra.  The  relation  between 
the  flame,  spark,  or  arc  spectra  and  the  chemistry  of  the  emitters  is  not 
known.  The  source  of  spectra,  like  that  from  the  blue  cone  of  a  Bunsen 
burner,  the  Swan  spectra,  is  at  present  unknown.  It  is  very  probable, 
however,  that  chemical  reactions  play  an  important  r61e  in  the  emission 
or  absorption  of  light  and  especially  of  band-spectra.  We  usually  think  of 
most  spectra  like  the  sodium  D  lines  as  coming  from  the  metallic  atoms 
of  sodium.  Fredenhagen1  points  out  that  under  most  conditions  oxygen 
is  present.  In  chlorine,  hydrogen,  or  fluorine  flames,  calcium,  strontium, 
thallium,  sodium,  barium,  and  copper  give  spectra  that  are  very  different 
from  those  obtained  when  oxygen  is  present.  Thallium  under  these  condi- 
tions does  not  show  the  characteristic  green  line,  and  the  D  sodium  lines 
are  completely  absent.  Work  upon  the  absorption  of  sodium,  mercury, 
potassium,  and  various  other  vapors  shows  that  the  presence  of  foreign  gases 
modifies  the  character  of  the  absorption  very  much.  Many  believe  that 
certain  series  or  groups  of  lines  are  due  to  chemical  reactions  of  various 
kinds. 

Chemical  reactions  and  processes  of  ionization  and  recombination  are 
believed  to  place  the  atom  or  molecule  in  a  peculiar  condition  by  means  of 
which  it  can  emit  energy  to  the  ether  or  absorb  energy  from  it.  Under 
ordinary  conditions  the  atom  does  not  seem  capable  of  doing  this.  In 
sodium-vapor,  for  instance,  theory  indicates  that  only  one  in  several  thou- 
sand of  the  sodium  atoms  are  taking  part  in  the  absorption  of  the  D  lines 
at  any  particular  instant.  The  problem  as  to  how  energy  is  transferred 
to  and  from  matter  is  then  one  of  the  fundamental  problems  of  science. 

Our  present  theory  of  the  mechanism  of  absorption  and  emission  of 
radiations  is  very  simple.  Light  and  heat  are  electromagnetic  radiations, 
and  hence  the  emitter  or  absorber  must  be  either  an  electric  charge  or  a 
magnetic  pole.  As  free  magnetic  poles  are  not  known  to  us  and  free  electric 
charges  are,  theory  makes  the  electric  charge  the  origin  of  all  electro- 
magnetic phenomena.  At  present  no  positive  electrical  charge  is  known 
to  be  associated  with  portions  of  matter  smaller  than  the  hydrogen  atom, 
whereas  negative  charges  or  electrons  are  known  to  be  associated  with 
charges  of  about  one  seventeen-hundredth  that  of  the  hydrogen  atom.  As 
far  as  experiment  shows,  these  electrons  always  have  the  same  properties 
and  the  same  charge,  no  matter  from  what  element  they  may  come.  It  is 
for  these  reasons  that  the  electron  is  made  the  basis  of  all  electromagnetic 
theory,  and  at  present  there  are  but  few  phenomena  that  can  not  be  ex- 
plained, if  explained  at  all,  by  this  theory. 

Radiations,  and  especially  light-radiations,  have,  then,  their  origin  in 
electric  charges.  Continuous  spectra  like  those  of  the  metals  are  due  to 
free  electrons  in  the  metals  and  have  little  connection  with  chemical  con- 
stitution. Fine  line-  and  band-spectra  apparently  are  due  to  different 
systems  of  electrons  within  the  atom,  and  are  greatly  affected  in  intensity 

1  Phys.  Zeit.,  8,  404,  729  (1907). 


10 


A   STUDY   OF   THE    ABSORPTION   SPECTRA. 


by  the  presence  of  neighboring  atoms.  The  electrons  of  this  type  vibrate 
in  definite  frequencies  that  can  be  changed  by  only  infinitesimal  amounts. 

ORGANIC   ABSORPTION  SPECTRA.— THE  UNIT    OF  THIS   ABSORPTION. 

In  discussions  concerning  the  color  of  organic  compounds  it  is  custom- 
ary to  speak  of  the  selective  absorption  as  being  due  to  certain  ions  or  mole- 
cules. This  is  probably  true  in  the  infra-red;  the  electric  charges  absorbing 
these  long  wave-length  radiations  being  probably  associated  with  masses 
of  molecular  size.  But  in  the  visible  and  ultra-violet  portions  of  the  spec- 
trum the  absorber  invariably  has  a  value  of  e/m  (e  the  charge,  and  m  the 
mass)  of  the  same  magnitude  as  that  of  the  electron.  Drude  l  has  investi- 
gated a  large  number  of  organic  compounds  and  shows  that  the  absorber 
of  all  the  shorter  waves  of  the  spectrum  is  the  negative  electron.  Hous- 

toun2  has  calculated  the  value  of  e/m  =  1.297  f  K   *      °  for  the  absorption 

xo 

bands  of  several  organic  compounds  and  also  shows  that  the  absorber  is 
the  electron,  (f  is  the  refractive  index,  K  the  maximum  value  of  the 
coefficient  of  extinction;  ^0  is  the  wave-length  of  maximum  absorption,  and 
^i  is  the  wave-length  for  which  the  coefficient  of  extinction  has  a  value 
equal  to  half  its  maximum.)  The  formula  used  is  based  on  the  present 
laws  of  dispersion. 

The  following  table  is  taken  from  Houstoun's  paper. 


Compound. 

*0 

e/m 

Fuchsin  in  alcohol  

5500 

1.8  (10)7 

Phloxin  in  water  

5150 

1.4  (10)7 

Crystal  violet  in  alcohol   .    .        ... 

5750 

4.9  (10)7 

Corallin  in  alcohol  

4650 

1.6  (10)' 

Methy  lene  blue  in  water  

6650 

5.4  (10)' 

Water  blue  in  water  

5750 

8  1  (10)6 

Eosin  blue  in  water  

5150 

6.9  (10)* 

Cyanine  in  alcohol  

5870 

5.8  (10)' 

Throughout  this  monograph,  then,  it  will  be  considered  that  the 
absorbers  are  negative  electrons.  These  electrons  have  certain  free  periods 
corresponding  to  bands  of  selective  absorption.  These  free  periods  are 
greatly  modified  by  the  presence  of  certain  chemical  radicles,  and  seem  to 
be  electrons  that  are  situated  either  in  the  outer  parts  of  the  atom  or  between 
two  or  more  atoms.  Stark  and  others  call  these  the  valency  electrons  and 
consider  that  chemical  valency  is  due  to  them.  Chemical  bonds  and  these 
electrons  will  therefore  be  closely  related.  As  an  aid  to  our  imagination 
we  will  consider  the  atoms  or  ions  as  large  spherical  regions  throughout 
which  a  positive  charge  is  uniformly  distributed.  These  regions  are  some- 
what similar  to  the  "spheres  of  influence."  Two  atoms  collide  when  their 
spheres  of  influence  touch  one  another.  Groups  of  atoms  comprising  ions, 
radicles,  or  molecules  will  also  have  spheres  of  influence.  No  ion  can  pene- 


1  Ann.  Phys.,  14,  677,  726,  936,  961  (1904). 

J  Nature,  80,  338  (1909);  Proc.  Roy.  Soc.,  A,  82,  606,  Sept.  18  (1909). 


INTRODUCTION.  11 

trate  the  sphere  of  influence  of  another  atom  or  molecule.  On  the  other 
hand  the  electrons  are  very  small  and  compare  in  relative  size  to  the  atom 
much  as  the  sun  compares  in  size  to  the  solar  system.  Electrons  can,  there- 
fore, move  through  ions  and  atoms  or  can  move  in  the  interatomic  spaces 
with  considerable  ease.  In  the  metals  a  large  number  of  electrons  are  free. 
In  organic  compounds  that  are  transparent  to  certain  wave-lengths  the 
electrons,  in  general,  will  be  held  within  certain  regions  by  forces  that  are 
elastic  in  their  nature;  that  is,  the  force  increases  in  proportion  to  the 
amount  the  electron  is  moved  from  its  position  of  equilibrium. 

THE   THEORY   OF    CHROMOPHORES. 

In  considering  absorption  spectra  it  is  often  quite  sufficient  to  speak 
qualitatively  of  the  color  of  different  compounds.  The  introduction  of  cer- 
tain groups  into  colorless  compounds  often  results  in  a  colored  compound. 
Any  such  group  is  a  chromophore.  Sometimes  the  chromophore  may  be 
weak  and  it  may  require  the  addition  of  several  chromophores  to  produce 
a  colored  compound.  Ultimately  the  color  is  due  of  course  to  absorbers 
existing  within  the  chromophore.  Among  the  better  known  chromophores 
are  the  groups: 

>C  =  C<  -CO  >C=NH  -CH  =  N-  -N  =  N- 


/ 


. 

-N/ 
^ 


ft 

O  X0 


The  structure  of  compounds  is  very  intimately  connected  with  their 
color,  and  by  means  of  color  differences  it  is  often  possible  to  differentiate 
isomers.  An  example  of  the  latter  case  is  the  following: 

C.H8  •  N-N  '  SO3K  C,H5  •  N  =  N  •  SO,K 

Syn-benzene-diazo-sulfonate,  orange.  Anti-benzene-diazo-sulfonate,  yellow. 

The  following  are  typical  examples  of  the  effect  of  chromophores: 

Colored.  Colorless. 

C.H.-N=N-C,H,        Azobenzene.  CaH»NH-NHC9H8  Hydrazobenzene. 

C6H8  -  N  =  O  Nitrosobenzene.  C.H,  -  N  •  H  •  OH    Phenylbydroxylamine. 

O  =  CeH4=O  Quinone.  HO  •  C,H«  •  OH  Hydroquinone. 

C.H.  •  CO  •  CO  •  CO  •  C.H?  C.H.  -  CO  •  CH,  •  CO  •  C8H. 

Diphenyltriketone.  Dibenzoylmethane. 

The  introduction  of  a  radical  into  an  organic  compound  usually  either 
weakens  the  color  or  increases  it.  An  interesting  question  comes  up  as  to 
whether  color-changes  are  in  any  way  related  to  energy  changes  in  these 
chemical  reactions.  A  bathochrome  causes  the  absorption  bands  to  be 
wider,  while  an  auxochrome  causes  the  intensity  of  the  absorption  to  be 
greater.  A  hypsochrome  causes  the  absorption  bands  to  narrow,  a  dimino- 


12  A    STUDY    OF   THE    ABSORPTION   SPECTRA. 

chrome  causes  the  coefficient  of  absorption  within  the  band  to  be  smaller. 
A  good  example  of  an  auxochrome  is  that  of  the  group  —  CO  —  C  «=  C  —  CO  — 
in  indigo: 

r\  TT  /         Nf1    P'  \p  TI 

l^jllfX.  /  =          \  /        •          < 

A  similar  rdle  is  played  by  the  same  auxochrome  in  the  deeply  colored 
compounds  similar  to  the  indigos: 

/cox       /co\ 

/COX 
C,H/       ^>C  = 

Alkyl,  aryl,  and  the  halogens  act  as  bathochromes;  while  the  acylenes 
CH3CO  and  C6H5CO  act  as  hypsochromes.  Kriiss  has  shown  that  CH,, 
OCH3,  C2H5  and  Br  shift  the  absorption  bands  to  the  red,  N02  and  NH2 
towards  the  violet. 

In  general,  the  color,  the  position  of  the  absorption  bands  and  the 
extinction  coefficients  vary  for  different  solvents.  In  many  cases  a  very 
plausible  explanation  is  to  assume  the  formation  of  chemical  compounds 
between  the  dissolved  salt  and  the  solvent. 

Benzene  and  its  derivatives  show  selective  absorption  in  the  ultra- 
violet. In  alcohol  the  benzene  absorption  consists  of  seven  bands  between 
X  2330  and  X  2710.  The  absorption  and  fluorescent  spectra  of  a  large  number 
of  compounds  containing  the  benzene  ring  have  been  investigated.  A  good 
example  is  that  of  anthracene.  This  shows  the  following  fluorescent  bands. 

Solid A  4250        X  4495        A  4745        A  4980        X  5300 

Solution A  4050        A  4275        A  4540        A  4820  

Vapor ;3900        X  4150        A  4320 

Benzene  gas  has  some  30  bands.    In  solution  the  bands  are  broad. 

The  bands  of  both  the  vapor  and  solution  are,  in  general,  shifted  to 
the  red  when  chlorine,  bromine,  the  methyl  group,  etc.,  replace  the  hydro- 
gen. The  shift  is  greater  the  greater  the  molecular  weight  of  the  entering 
atom  or  group.  The  bands  of  benzene  that  are  shifted  are  those  that  are 
common  to  benzene,  toluene,  ethylbenzene,  and  oxyxylene,  and  are  un- 
affected by  temperature  and  pressure. 

Hartley  gives  the  following  wave-lengths  for  these  bands: 

In  solution.. A  2682  ;  2657-2642  A  2614-2600  A  2539  X  2480  i  2426. 5  A  2376 
In  vapor....;  2670  ;  2630  A  2590  ;.  2523  A  2466  A  24 11  A  2360 

The  substitution  products  of  benzene  have  much  less  characteristic 
spectra  than  benzene  itself. 

THEORY   OF    DYNAMIC    ISOMERISM. 

Baly  and  others  have  recently  supported  the  view  that  the  absorption  of 
light  by  organic  compounds  does  not  take  place  under  ordinary  conditions, 
but  that  absorption  takes  place  when  there  is  a  change  in  the  way  in  which 


INTRODUCTION.  13 

the  atoms  are  united,  as  when  a  chemical  compound  is  transformed  into  an 
isomeric  form.  This  dynamic  isomerism  is  known  to  take  place  in  many 
chemical  compounds  in  the  presence  of  a  catalytic  agent  or  at  high  tem- 
peratures. The  case  of  acetylacetone  and  ethyl  acetoacetate  is  cited  as  an 
example.  The  absorption  in  this  case  is  considered  as  being  due  to  the  reac- 
tion changing  the  ketonic  (1)  to  the  enolic  (2)  form. 
H  H 

_C  —  C—    +±    —  C  =  C  — 


HOD 


OH  (2) 

It  has  been  found  that  anything  that  changes  the  velocity  of  the  above 
reaction  also  changes  the  persistence  of  the  absorption  bands. 

The  case  of  pyruvic  ester  is  also  given  as  a  typical  example  of  this  kind 
of  a  reaction  which  results  in  the  absorption  of  light. 

CH3—  C—  C—  O  CiHj    +±    CHS—  C=C—  O  C2H5 

II     li  II 

O    O  0-0 

This  oscillation  of  the  carbonyl  grouping  Stewart  and  Baly  call  isor- 
ropesis. 

On  account  of  the  large  number  of  isomeric  compounds  that  may  exist 
among  the  hydrocarbons,  it  is  easily  seen  that  a  theory  of  this  kind  may 
have  very  wide  applicability. 

THEORY   OF   STARK. 

Stark  considers  that  chemical  valency  can  be  explained  as  due  to  the 
presence  of  negative  electrons  between  the  atoms,  or  rather  the  positively 
charged  ions  that  constitute  atoms  when  they  are  combined  with  one  or 
more  electrons.  These  valency  electrons  are  considered  as  being  "  locked" 
to  the  atoms  in  different  degrees.  Whenever  a  double  chemical  bond  exists 
in  a  compound  it  is  considered  that  one  or  more  of  the  valency  electrons  is 
very  loosely  united  with  the  atom.  Under  certain  conditions,  as,  for  example, 
when  ultra-violet  light  falls  on  a  compound,  some  of  the  electrons  may 
absorb  sufficient  energy  to  be  shot  off  from  the  molecule.  In  this  way  the 
photoelectric  is  explained.  When  an  electron  is  attracted  back  to  a  mole- 
cule which  has  lost  one,  Stark  supposes  that  light  will  be  emitted,  and  in  this 
way  fluorescence  can  be  explained.  The  fluorescence  of  a  large  number  of 
organic  compounds  has  been  investigated  by  Stark  and  Steubing.1 

COMPLEXITY  OF  THE  PROBLEM   OF  THE   SPECTRA  OF  COMPOUNDS. 

It  is  a  fact  that  investigations  on  the  spectral  emission  and  absorption 
of  bodies  have  been  far  less  fruitful  in  extending  our  knowledge  of  the 
structure  of  the  atom  than  had  been  expected.  This  is  largely  owing  to  the 
almost  infinite  complexity  of  the  structure  of  the  atom  and  our  general 
ignorance  of  the  forces  that  exist  there.  Probably  the  best  known  example 
is  that  of  the  uranyl  group  which  we  shall  describe.  Let  us  consider  the  spec- 

1  Phys.  Zeit.,  9,  661  (1908);  9,  481  (1908). 


14  A    STUDY   OP   THE    ABSORPTION    SPECTRA. 

tral  vibrations  that  can  be  produced  by  components  that  exist  or  may  be 
produced  from  the  apparently  simple  UO2  group: 

(1)  We  have  the  absorption  spectrum  described  above.    At  low  tem- 
peratures most  of  these  bands  break  up  into  much  finer  bands. 

(2)  The  uranyl  salts  under  various  methods  of  excitation  emit  a  phos- 
phorescent spectrum  of  a  large  number  of  rather  fine  bands  throughout  the 
visible  region  of  the  spectrum.    It  is  quite  possible  that  this  spectrum  is 
intimately  connected  with  that  of  the  absorption  spectrum. 

(3)  We  have  the  absorption  spectrum  of  the  uranous  salts  which  has 
been  described  above.     This  spectrum  has  been  probably  caused  by  the 
change  of  valency  of  the  uranium  atom.    Uranium  is  known  to  form  quite 
a  large  number  of  oxides,  and  it  is  quite  possible  that  for  each  valency  of 
the  uranium  we  have  a  characteristic  spectrum.    (This  also  is  being  inves- 
tigated.)   It  is  also  quite  probable  that  at  lower  temperatures  those  spectra 
would  consist  of  quite  fine  bands. 

(4)  We   have  the   spark  spectrum   and   the  absorption  spectrum  of 
oxygen,  and 

(5)  that  of  ozone,  which  bears  no  relation  to  that  of  oxygen. 

(6)  There  is  the  exceedingly  complex  spark  spectrum  of  uranium,  con- 
sisting of  thousands  of  fine  lines,  and  also 

(7)  the  complex  arc  spectra.     From  radioactive  experiments  it  is 
known  that  uranium  is  continually  breaking  down  into  ionium. 

(8)  Ionium  possesses  the  properties  of  a  chemical  element  and  most 
likely  has  a  spectrum  of  its  own.    This  would  make  eight  spectra. 

(9)  Ionium  breaks  down  into  radium  and  radium  has  a  very  charac- 
teristic spark  spectrum,  as  does  also 

(10)  the  radium  emanation.     During  the  various  radioactive  trans- 
formations several  a-particles  are  emitted  with  a  velocity  almost  as  great 
as  that  of  light.    It  is  probable  that  these  particles  are  moving  with  very 
great  velocities  in  the  uranium  atom  under  ordinary  conditions. 

(11)  The  a-particles  are  known  to  be  charged  helium  atoms  and  there- 
fore under  proper  excitation  would  give  the  helium  spectrum.    The  radium 
emanation  breaks  down  into  radium  A,  B,  C,  D,  E,  and  F.    These  products 
behave  like  chemical  elements  and  probably  have  characteristic  spectra. 

(12)  The  final  product  is  lead,  which  has  very  complex  spark  and  arc 
spectra.    During  these  transformations  several  electrons  have  been  thrown 
off  from  the  various  products  with  enormous  velocities.     In  a  very  large 
number  of  the  above  spectrum  lines  the  Zeeman  effect  indicates  the  pres- 
ence of  negative  electrons  and  charged  doublets. 

We  thus  see  what  an  extremely  complex  system  the  group  U02  must 
be,  and  it  might  seem  almost  hopeless  to  disentangle  the  mystery  of  its 
various  spectra.  At  present  we  know  that  the  arc-  and  spark-spectra  problem 
is  very  complex  and  that  we  have  very  few  methods  of  producing  any 
changes  in  them.  Practically  the  only  method  of  changing  the  frequency 
of  these  vibrations  is  by  applying  a  very  powerful  magnetic  field  or  great 
pressure  and  these  changes  in  the  frequency  are  very  small.  One  very 
important  result,  however,  has  been  obtained  by  Kayser,  Runge,  Wood, 
and  others.  This  work  consists  in  separating  spectrum  lines  into  various 


INTRODUCTION.  15 

series.  A  series  of  lines  comprises  those  whose  intensity  and  Zeeman  effect 
vary  in  the  same  way  when  the  conditions  outside  the  atom  are  changed. 
The  work  of  Wood  is  important  as  showing  that  spectrum  lines  are  due  to 
different  systems  of  vibrators  inside  the  atom.  By  using  monochromatic 
light  of  different  wave-lengths  he  has  been  able  to  excite  different  series  of 
lines  which  constitute  altogether  the  fluorescent  spectrum  of  the  element. 

Present  theories  of  the  atom  usually  regard  the  electrons  and  other 
vibrators  that  are  the  sources  of  arc  and  spark  lines  as  being  well  within  the 
atom,  and  as  affected  by  external  physical  conditions  only  under  very  special 
circumstances.  Stark  believes  that  these  electrons  may  rotate  in  circular 
orbits,  the  locus  of  the  centers  of  these  orbits  being  a  closed  curve,  say  a 
circle.  This  system  will  be  equivalent  to  a  positive  or  negative  charge 
according  to  the  sense  of  rotation  of  these  electrons.  These  electrons  we 
will  call  ring  electrons.  Supposing  these  systems  to  be  positive  charges,  it 
will  require  electrons  to  neutralize  these  charges.  Several  of  these  neutral- 
izing electrons  may  be  in  the  outer  parts  of  the  atom  and  under  certain 
conditions  might  be  knocked  off  from  the  atom.  These  easily  removable 
electrons  will  be  called  "valency  "  electrons,  and  can  exist  under  different 
conditions  of  "  looseness  "  of  connection  with  the  atom.  Most  of  the  neu- 
tralizing electrons  will  probably  lie  far  within  the  atom.  For  instance,  we 
would  expect  that  in  the  uranium  atom  the  charged  helium  atoms  are 
neutralized  by  negative  electrons. 

Our  theory  is  that  the  finer  absorption  bands  of  such  salts  as  neo- 
dymium,  erbium,  and  uranium  are  due  to  vibrations  of  these  neutralizing 
electrons,  and  that  the  forces  acting  upon  these  are  considerably  different 
from  those  acting  on  the  ring  electrons,  which,  in  many  cases,  give  a  normal 
Zeeman  effect.  It  is  probable  that  these  neutralizing  electrons  play  the 
greatest  r61e  in  the  optical  properties  of  bodies,  such  as  the  properties 
determining  the  index  of  refraction,  the  extinction  coefficient,  etc. 

Usually  the  equation  of  motion  of  such  an  electron  is  given  by  an  equa- 
tion like  the  following  when  a  light-wave  of  an  electric  field  E  cos  pt  is  pass- 
ing by  it: 

m-^+k-^+ri*x=*E  cospt 

where  m  is  the  total  mass  (electromagnetic  and  material)  of  the  electron, 
k  dxjdt  is  the  damping  or  fractional  term,  and  n2x  is  the  quasi-elastic  force. 
It  is  an  experimental  fact,  as  shown  by  the  above  work  and  the  work  of 
other  investigators,  that  k  and  n2  are  not  only  functions  of  the  electron 
and  the  atom,  but  that  they  are  also  functions  of  the  physical  and  chemical 
conditions  existing  in  the  neighborhood  of  the  atom. 

On  the  other  hand,  the  effect  on  k  and  n2  for  a  ring  electron,  when 
external  physical  and  chemical  conditions  are  changed,  is  very  small.  It 
is  for  this  reason,  and  the  probable  fact  that  there  are  relatively  few  neu- 
tralizing electrons,  that  we  believe  that  much  greater  progress  can  be  made 
in  determining  some  of  the  properties  and  constitution  of  various  intera- 
tomic systems  of  atoms  and  molecules  by  the  study  of  the  absorption  spectra 
of  uranium  and  neodymium  than  by  a  study  of  the  arc-  or  spark-spectra  of 
the  same. 


16  A    STUDY   OF   THE    ABSORPTION  SPECTRA. 


METHOD  OF  ATTACKING  THE  PROBLEM  OF  EMISSION  AND 
ABSORPTION   SPECTRA. 

The  method  of  attacking  the  above  problem  will  be  to  study  the  effect 
on  the  spectra  of  a  body  produced  by  changing  the  physical  and  chemical 
conditions  about  the  light  absorbers  or  emitters  within  as  wide  ranges  as 
possible.  Some  of  the  possible  changes  that  can  be  made  are  as  follows: 
Take,  for  instance,  the  uranyl  group  UO2.  We  can  find  the  effect  upon 
the  absorption  bands  produced  (1)  by  diluting  the  solution,  (2)  by  changing 
the  acid  radical  to  which  the  uranyl  group  is  united,  (3)  by  changing  the 
solvent  and  using  mixtures  of  solvents,  (4)  by  adding  other  salts  (like 
aluminium  chloride),  or  (5)  by  adding  acids  of  the  same  kind  as  that  of  the 
salt  of  the  uranyl  group.  The  effect  (6)  of  adding  foreign  salts  and  acids 
at  the  same  time  and  then  varying  the  solvent,  or  the  temperature,  can 
also  be  tried.  In  this  way  a  very  large  number  of  very  interesting  things 
can  be  tested.  In  most  of  these  changes  Ic  will  be  kept  constant. 

In  the  above  example  the  temperature  (7),  the  external  pressure  (8), 
the  electric  field  (9),  and  the  magnetic  field  (10)  can  be  changed  between 
wide  limits.  The  latter  effect  is  a  very  important  one.  For  example,  in 
aqueous  solution  neodymium  salts  give  a  large  number  of  fine  bands,  in 
glycerol  there  are  quite  a  number  of  new  bands  replacing  the  "  water  " 
bands,  and  in  the  alcohols  there  are  various  "  alcohol  "  bands.  At  low 
temperatures  these  bands  become  very  fine  and  it  is  quite  possible  to  detect 
the  Zeeman  effect.  Now  it  seems  quite  probable  that  a  "glycerol  "  band 
and  an  "  alcohol  "  band  that  seem  to  replace  each  other  as  the  solvent  is 
changed  are  both  due  to  the  same  vibrator.  If  the  Zeeman  effect  is  the 
same  in  both  cases  it  would  be  a  strong  argument  in  favor  of  the  above 
theory.  A  case  that  will  soon  be  described  is  very  important.  It  was 
found  that  the  wave-lengths  of  certain  neodymium  lines  in  a  pure  aqueous 
solution  did  not  change  when  the  temperature  was  raised  from  0°  to  90°. 
If,  however,  calcium  chloride  was  added,  then  on  raising  the  temperature 
the  above  bands  were  shifted  to  the  red.  A  very  interesting  and  important 
investigation  is  whether  the  Zeeman  effect  on  the  band  would  be  affected 
by  the  presence  of  substances  like  calcium  chloride. 

To  be  compared  with  the  above  changes  are  changes  in  the  absorption 
spectra  of  the  crystals  of  the  salt  (11)  as  affected  by  water  of  crystallization, 
or  by  the  presence  of  foreign  substances,  or  as  affected  by  the  polarization 
(12)  or  direction  of  passage  of  light  through  the  crystal.  The  absorption 
spectra  (13)  of  the  anhydrous  powder  at  different  temperatures,  etc.,  should 
be  found.  The  phosphorescent  spectrum  (14)  should  be  studied  in  this 
connection,  especially  as  affected  by  the  mode  of  stimulation  (X-rays, 
cathode  rays,  heating,  or  monochromatic  light  of  different  wave-lengths). 
The  temperature,  electric  or  magnetic  field  could  be  changed  about  the 
phosphorescing  body.  The  effect  of  change  of  state  (15)  should  be  tried  if 
this  is  possible,  also  any  possible  changes  of  valency  of  the  atoms  (16)  com- 
posing the  body  investigated.  It  is  very  important  that  these  suggested 
modes  of  attack  should  be  extended  throughout  the  whole  range  of  wave- 
lengths. 


INTRODUCTION.  17 

After  correlating  the  data  obtained  by  the  above-named  investigations 
it  is  pretty  certain  that  it  will  be  possible  to  take  each  vibrator  and  trace 
the  effects  produced  upon  it  by  the  above  changes.  It  is  highly  probable 
that  we  shall  also  know  something  of  the  nature  of  the  vibrating  system 
and  the  part  that  it  plays  in  that  complex  body  we  call  the  atom. 

For  instance,  let  us  take  the  bands  of  uranyl  nitrate.  It  was  found 
that  the  uranyl  bands  of  an  aqueous  solution  of  the  nitrate  had  shorter 
wave-lengths  than  that  of  any  other  uranyl  salt  in  water.  The  uranyl  bands 
of  the  nitrate  in  other  solvents  were  farther  towards  the  red  than  the  bands 
of  an  aqueous  solution.  Now,  although  the  solvent  has  a  great  effect  upon 
the  bands,  nevertheless  it  seems  quite  certain  that  the  NO3  group  has  a 
very  considerable  effect  upon  the  vibrations  of  the  uranyl  group.  If  it 
were  possible  to  find  the  ratio  elm  for  the  vibrators  in  this  case  by  the 
Zeeman  effect,  it  might  be  possible  to  find  an  approximate  value  for  the 
force  exerted  by  the  NO3  group  upon  the  vibrator.  It  seems  quite  certain 
that  this  force  differs  for  the  vibrators  producing  different  bands.  The 
measurements  of  the  wave-lengths  of  the  uranous  bands  are  as  yet  very 
few,  yet  they  seem  to  indicate  that  for  aqueous  solutions  of  the  uranous 
salts  the  bands  of  the  nitrate  are  farther  towards  the  violet  than  the  bands 
of  the  other  uranous  salts.  The  values  given  for  the  phosphorescent  bands 
by  E.  Becquerel  and  by  J.  Becquerel  indicate  that  the  bands  of  the  nitrate 
are  further  towards  the  violet  than  those  of  the  other  uranyl  salts.  We 
thus  see  that  throughout  these  three  spectra  the  NOS  group  exerts  a 
similar  force  upon  the  vibrators  that  are  the  cause  of  the  bands. 


CHAPTER  II. 

EXPERIMENTAL  METHODS. 

In  this  work  the  methods  used  by  Jones  and  Uhler  *  and  Jones  and 
Anderson  2  have  in  the  main  been  employed. 

The  investigations  of  the  effect  of  changes  in  temperature  on  the 
absorption  spectra  of  solutions  have  been  confined  to  different  concentra- 
tions of  aqueous  solutions  of  the  chloride,  nitrate,  acetate,  sulphate,  and 
sulphocyanate  of  cobalt,  the  chloride,  acetate,  and  sulphate  of  nickel,  the 
chloride,  sulphate,  and  acetate  of  chromium,  chrome  alum,  the  nitrate  and 
bromide  of  copper,  uranous  chloride,  erbium  chloride,  the  chloride  and 
nitrate  of  praseodymium,  the  sulphate,  acetate,  chloride,  and  nitrate  of 
uranyl,  and  the  chloride,  bromide,  and  nitrate  of  neodymium.  Spectro- 
grams of  the  absorption  spectra  for  a  given  concentration  of  a  salt,  with  a 
constant  thickness  of  layer,  have  been  made  for  every  15°  between  0°  and 
90°  C. 

To  make  a  spectrogram,  light  from  a  Nernst  glower  and  from  a  spark 
is  allowed  to  pass  through  the  solution  that  is  being  investigated.  It  is 
then  focused  upon  the  slit  of  a  spectroscope,  and,  falling  on  a  concave 
grating,  is  spread  out  into  a  spectrum  on  the  film  upon  which  it  is  photo- 
graphed. The  films  used  were  made  by  Wratten  and  Wainwright,  of 
Croyden,  England,  and  were  very  uniformly  sensitive  to  light  from  ^  2100 
to  X  7200. 

The  sectional  diagram  (fig.  1)  will  make  the  experimental  arrange- 
ment of  the  apparatus  clearer.  N  is  a  Nernst  glower  which  is  arranged  to 
slide  along  the  rod  AB.  P  and  P'  are  quartz  prisms  which  are  held  by  a  lid 
L.  The  prism  P  is  stationary,  whereas  the  prism  P'  can  be  moved  by  the 
traveling  carriage  E  back  and  forth  through  the  trough  T,  which  contains 
the  solution  whose  absorption  spectrum  is  being  investigated.  AB  is  so 
inclined  that  the  optical  length  of  the  light-beam  from  N  to  P',  P  and  the 
concave  mirror  M  shall  be  constant,  whatever  the  length  of  the  solution 
between  P  and  P'  may  be.  The  greatest  length  of  path  PP'  used  was  200 
mm.  The  hypothenuse  faces  of  P  and  P'  are  backed  by  air  films  which  are 
inclosed  by  glass  plates  cemented  to  the  quartz  prisms. 

Considerable  difficulty  was  experienced  in  finding  a  cement  that  would 
adhere  to  the  polished  quartz  prisms  at  the  higher  temperatures.  For 
aqueous  solutions  baked  caoutchouc  was  found  to  work  fairly  well.  Among 
the  various  cements  that  may  prove  successful  is  bakelite.8  This  is  briefly 
described  as  being  made  of  equal  amounts  of  phenol  and  formaldehyde  to 
which  a  small  amount  of  an  alkaline  condensing  agent  is  added.  This 
latter  is  a  compound  made  of  ammonium  carbonate,  soap,  sodium  carbonate, 

1  Carnegie  Institution  of  Washington  Publication  No.  60. 

2  Ibid.,  No.  110. 

1  Journ.  Ind.  and  Eng.  Chem.  (March),  p.  156  (1909). 

19 


20 


A    STUDY   OF   THE    ABSORPTION    SPECTRA. 


and  potassium  cyanide.  The  solution  should  be  gently  heated.  The  lower 
layer  of  liquid  is  used  for  the  cement  and  is  heated  for  several  hours  at  a 
temperature  of  160°  under  the  pressure  of  100  pounds  per  square  inch. 

D  is  a  brass  box  holding  the  trough  T.  D  is  filled  with  oil  and  is  placed 
in  a  water-bath  whose  temperature  can  be  varied  between  0°  and  90°  C. 
The  path  of  the  beam  of  light  is  then  from  the  Nernst  glower  N  or  spark 
to  the  quartz  prism  P'.  The  light  is  totally  reflected  from  the  hypothenuse 
face  of  this  prism  through  the  solution  to  P.  This  prism  also  has  its  hy- 
pothenuse face  backed  by  an  air-film,  so  that  the  light  is  totally  reflected 
upwards  to  the  concave  speculum  mirror  at  M.  M  focuses  the  light  on  the 


slit  of  the  Rowland  concave  grating  spectroscope,  G  being  the  grating  and 
C  the  focal  curve  of  the  spectrum.  The  prism  arrangement  was  designed 
by  Dr.  John  A.  Anderson. 

When  the  quartz  prisms  were  being  set  up  for  temperature  work  a  very 
peculiar  set  of  images  were  obtained  that  the  writers  have  not  yet  fully 
understood,  although  the  optics  is  probably  quite  simple.  When  a  Nernst 
filament  is  observed  through  one  of  the  prisms  so  that  the  incident  beam 
of  light  is  symmetrical  to  the  prism,  there  is  but  one  image  of  the  filament 
to  be  seen.  If  now  the  prism  is  rotated  in  general  three  images  will  be 
seen.  For  a  certain  position  of  the  prism  the  three  images  are  of  practi- 
cally the  same  intensity. 


EXPERIMENTAL   METHODS.  21 

This  apparatus  was  found  to  work  very  well  for  aqueous  solutions. 
Some  evaporation  took  place  at  the  higher  temperatures,  but  distilled 
water  was  added  in  proper  quantity  and  mixed  with  the  solution  so  as  to 
keep  the  concentration  constant.  By  using  troughs  of  different  lengths  it 
was  possible  to  vary  the  length  of  salt  solution  through  which  the  light 
beam  passed  from  1  to  200  mm.  One  inconvenience  was  experienced  at 
low  temperatures;  moisture  would  sometimes  condense  upon  the  exposed 
prism-faces.  To  overcome  this  an  air-blast  was  directed  upon  these  faces, 
and  this  helped  very  materially  to  prevent  the  condensation  of  moisture. 

For  the  investigation  of  glycerol  and  other  solutions  a  cell  made  of 
fused  silica  was  used.  The  cell,  as  received  from  the  Silica  Syndicate  Com- 
pany, did  not  have  plane  parallel  ends.  At  the  suggestion  of  Dr.  Pfund 
these  were  ground  down  with  finely  powdered  emery  and  rouge.  In  this 
way  a  very  serviceable  cell  was  obtained.  The  depth  of  liquid  in  the  cell 
was  104  mm. 

For  work  on  the  effect  of  high  temperatures  on  absorption  spectra, 
a  closed  steel  cell  is  being  made.  This  is  intended  to  stand  the  pressures 
exerted  by  the  alcohols,  acetone,  ether,  water,  etc.,  at  their  critical  tem- 
peratures. The  ends  contain  quartz  windows  and  the  whole  interior  of 
the  cell  will  be  lined  with  gold.  At  the  same  time  a  radiomicrometer  is 
being  made  and  an  apparatus  is  being  devised  by  means  of  which  quanti- 
tative measurements  of  the  energy  absorption  for  all  parts  of  the  spectrum 
can  be  obtained. 

In  the  case  of  solids,  the  time  of  exposure  is  necessarily  long,  usually 
occupying  several  hours.  It  is  very  necessary  in  this  case  to  screen  off 
stray  light.  The  method  is  very  simple,  consisting  in  focusing  by  means 
of  mirrors  or  lenses  the  light  from  a  Nernst  glower  or  an  arc  upon  the  salt. 
The  salt  is  placed  a  short  distance  from  the  slit  of  the  spectroscope,  so  that 
the  directly  reflected  light  does  not  enter  the  slit.  By  this  means  only  the 
diffusely  reflected  light  enters  the  slit,  and  in  general  this  light  has  pene- 
trated somewhat  into  the  salt  and,  accordingly,  some  wave-lengths  are 
partly  or  wholly  absorbed.  The  salt  is  placed  at  such  a  distance  that  the 
grating  is  completely  filled  with  the  beam  of  diffusely  reflected  light  enter- 
ing the  slit.  This  method  has  been  used  by  several  investigators,  notably 
by  Anderson  1  and  Schultz.2 

The  observations  on  the  phosphorescence  of  uranium  compounds 
were  made  with  the  Hilger  spectroscope,  from  which  wave-lengths  can  be 
read  directly.  Either  sunlight  or  the  light  from  a  spark  was  used  as  the 
source  of  light  by  means  of  which  the  phosphorescence  could  be  excited. 
Screens  of  variously  colored  glasses  were  used  in  order  to  find  whether  the 
wave-length  of  the  exciting  light  had  any  effect  upon  the  phosphorescent 
spectrum.  Especially  valuable  was  a  glass  screen  3  that  absorbed  all  wave- 

1  Astrophys.  Journ.,  26,  73  (1907). 

2  Diss.,  Johns  Hopkins  University,  June  (1908). 

8  This  glass  screen  is  very  useful  for  observing  Haidinger's  brushes.  These  brushes 
as  seen  by  the  naked  eye  are  yellow  and  purple.  Using  a  blue-glass  screen  the  yellow 
fringes  become  dark  and  show  no  color.  With  the  above-mentioned  screen  the  brushes 
are  red.  These  facts  corroborate  the  theory  given  by  G.  G.  Stokes:  Collected  Papers, 
2,  p.  362. 


22  A   STUDY   OP  THE    ABSORPTION  SPECTRA. 

lengths  except  the  red,  blue,  and  violet.  When  this  was  used  no  yellow 
or  green  light  fell  upon  the  phosphorescing  uranium  salt,  so  that  any  light 
in  the  yellow  and  green  was  necessarily  due  to  phosphorescence  and  not  to 
reflection.  A  Fuess  monochromatic  illuminator  was  also  used,  sunlight 
or  arc-light  being  focused  upon  the  slit  of  the  illuminator.  The  salt  was 
placed  in  the  beam  of  transmitted  light.  Usually  the  region  of  spectrum 
used  was  50  or  100  Angstrom  units  wide.  The  phosphorescent  light  was 
viewed  with  the  Hilger  spectroscope. 

In  the  work  on  the  Zeeman  effect,  the  large  electromagnet  described 
by  Reese  was  used.  This  electromagnet  has  very  large  pole-pieces.  A 
cell  to  hold  the  solution  was  made  of  thin  cover-glass  plates  about  1.2  by 
1.2  by  0.3  cm.  in  size.  The  light  from  an  arc  or  a  Nernst  glower  was  focused 
upon  the  solution  by  means  of  lenses,  and  the  emergent  beam  of  light 
focused  upon  the  slit  of  the  spectroscope. 

The  concave  grating  described  above  was  used  for  mapping  the  absorp- 
tion spectra  of  solutions.  A  plane  Rowland  grating  was  also  employed  for 
visual  work  in  the  second  and  third  orders  of  the  spectrum.  For  polar- 
izing the  incident  light  Nicol  prisms  were  used. 

When  anhydrous  salts  were  employed  they  were  dried  in  every  case 
by  the  best  methods  available.  Thus,  chlorides  were  dried  in  a  current  of 
hydrochloric  acid,  bromides  in  a  current  of  hydrobromic  acid  gas,  and  so  on. 

The  usual  precautions  were  taken  in  working  with  nonaqueous  solvents 
to  keep  out  all  traces  of  moisture.  Dehydrated  salts  were,  of  course,  pro- 
tected from  contact  with  the  air. 

An  attempt  was  made  to  obtain  the  electrostatic  Zeeman  effect.  For 
solutions  condensers  made  of  ordinary  cover-glass  slides  (used  in  mounting 
sections  for  microscopic  examination)  were  used.  Aluminium  foil  was 
placed  between  the  glass  slides  in  alternate  layers.  The  solution  (for 
instance,  neodymium  chloride  in  glycerol)  to  be  investigated  was  placed 
between  the  slides  between  which  there  was  no  foil.  For  the  production  of 
an  electric  field  a  Holtz  machine  was  employed.  This  experiment  was  tried 
for  several  solutions  and  for  one  gas,  nitric  oxide.  In  no  case  could  any 
difference  be  observed  when  the  electric  field  was  on  and  when  it  was  off. 
Further  work  is  being  done  in  this  direction,  especially  on  gases  such  as 
iodine,  bromine,  nitric  oxide,  etc.  In  this  way  enormous  electric  fields 
may  be  obtained,  and  it  is  not  difficult  to  make  the  light  pass  either  normal 
or  parallel  to  the  electric  field. 

In  describing  portions  of  the  spectrum,  red  will  be  considered  as  extend- 
ing from  X  9000  to  A  6500;  orange  from  X  6500  to  /I  6000;  yellow  from  X  6000 
to  >l  5750;  green  from  X  5750  to  X  5000;  blue  from  >l  5000  to  X  4500;  indigo 
from  A  4500  to  X  4250;  violet  from  X  4250  to  A  4000,  and  the  ultra-violet  from 
A  4000  to  A  1800.  Rays  of  greater  wave-length  than  X  9000  will  be  in  the 
infra-red.  These  rays  include  heat  rays  and  "  reststrahlen  "  and  have  been 
extended  to  a  wave-length  of  about  0.1  mm.  Hertzian  waves  have  been 
explored  from  wave-lengths  of  many  meters  to  that  of  about  6  mm.,  leaving 
thus  but  a  small  gap  between  electromagnetic  waves  produced  by  ordinary 
mechanical  devices  and  waves  produced  apparently  by  molecular  aggre- 
gates. Waves  of  shorter  wave-length  than  X  1800  will  be  designated  as 
Schumann  waves. 


CHAPTER  III. 

POTASSIUM  SALTS. 

Potassium  chromate. — Potassium  dichromate. — Potassium  ferro- 
cyanide. — Potassium  ferricyanide. 

Most  potassium  salts  in  solution  are  colorless,  and  for  this  reason  it  is 
considered  that  the  potassium  atoms  do  not  themselves  absorb  any  light 
in  the  visible  portion  of  the  spectrum.  Several  colored  potassium  salts 
are  known  and  the  colors  of  these  are  due  in  some  way  to  the  other  atoms 
in  the  salt  molecules.  In  the  present  work  the  absorption  spectra  of  potas- 
sium ferricyanide,  potassium  ferrocyanide,  potassium  chromate,  and  potas- 
sium dichromate  have  been  studied. 

Using  a  3-mm.  length  of  solution  of  potassium  ferricyanide  in  water 
we  find  that  for  a  normal  concentration  there  is  complete  absorption  of  all 
the  shorter  wave-lengths  of  light  beyond  A  4800.  As  the  concentration  is 
decreased  the  edge  of  transmission  moves  continually  towards  the  violet. 
It  should  be  noticed  that  the  region  between  complete  absorption  and 
complete  transmission  for  the  more  concentrated  solutions  is  quite  narrow, 
being  less  than  40  Angstrom  units;  solutions  of  this  salt  being  thus  quite 
good  screens  for  absorbing  light.  Continually  decreasing  the  concentration 
we  reach  a  0.0156  normal  solution,  when  a  transmission  band  begins  to 
appear.  For  a  certain  range  of  concentration  there  appears  an  absorption 
band  in  the  region  A  4200.  Further  decrease  in  concentration  results  in 
increasing  transmission  throughout  the  violet  and  ultra-violet.  For  dilu- 
tions greater  than  0.00195  normal  there  is  almost  complete  transmission 
throughout  the  ultra-violet.  Very  faint  bands  appear  in  the  regions  AA  2500 
to  2600,  AA  2950  to  3050  and  AA  3200  to  3250. 

Several  spectrograms  were  made  of  solutions  for  which  the  product 
of  concentration  and  depth  of  layer  were  kept  constant.  In  this  case  the 
spectrograms  will  be  identical  if  Beer's  law  holds.  According  to  this  method 
of  testing,  Beer's  law  was  found  to  hold  within  the  ranges  of  concentration 
over  which  the  spectrum  was  mapped. 

The  absorption  of  aqueous  solutions  of  potassium  ferrocyanide  was 
investigated  in  the  same  way.  A  half-normal  solution  3  mm.  deep  shows 
that  all  light  of  wave-lengths  shorter  than  A  3950  is  absorbed.  Keeping  the 
depth  of  layer  the  same,  it  is  found  that  with  decrease  in  concentration  the 
transmission  gradually  moves  towards  the  ultra-violet,  and  for  dilutions 
greater  than  0.0078  normal  there  is  transmission  throughout  the  whole 
spectrum.  Beer's  law  was  found  to  hold. 

A  2  normal  aqueous  solution  of  potassium  chromate  3  mm.  in  thickness 
shows  complete  transmission  of  wave-lengths  greater  than  A  4950.  Decreas- 
ing the  concentration  causes  the  transmission  to  move  gradually  towards 
the  violet,  and  for  a  0.01  normal  solution  a  transmission  band  appears  at 
A  3100,  or,  in  other  words,  there  appears  an  absorption  band  whose  center 
is  about  A  3700.  As  the  concentration  decreases  this  absorption  band  fills 


24  A    STUDY   OP   THE    ABSORPTION  SPECTRA. 

up,  the  violet  edge  of  the  transmission  band  gradually  pushes  out  into  the 
ultra-violet,  and  for  dilutions  greater  than  0.0005  normal  there  is  complete 
transmission  throughout  the  spectrum.  Beer's  law  was  found  to  hold  for 
potassium  chromate  throughout  the  above  ranges  of  concentration,  except 
in  the  more  concentrated  solutions  between  2  normal  and  0.25  normal. 

Potassium  dichromate  in  water  was  found  to  have  a  much  greater 
absorbing  power  than  the  solutions  previously  described.  A  one-third 
normal  solution  absorbed  all  wave-lengths  shorter  than  A  5350.  As  the 
concentration  is  decreased  the  transmission  extends  farther  and  farther 
out  into  the  violet.  For  a  0.0026  normal  concentration  a  transmission 
band  appears  in  the  violet,  thus  giving  an  absorption  band  whose  center 
is  about  ^  3800.  As  the  concentration  is  further  decreased  transmission 
becomes  greater  and  greater  in  the  violet  and  ultra-violet,  and  is  practically 
complete  for  a  0.0006  normal  concentration.  Beer's  law  has  been  tested 
between  the  above  ranges  of  concentration  and  has  been  found  to  hold. 

In  photometric  measurements  to  test  Beer's  law,  the  equation  denn- 
ing the  quantities  to  be  measured  is 


where  J0  is  the  intensity  of  the  light  that  enters  the  solution  (neglecting 
any  loss  due  to  reflection),  J  the  intensity  of  the  light  as  it  leaves  the  solu- 
tion, c  the  concentration  in  gram  molecules  of  the  salt  per  liter  of  solution, 
I  the  thickness  of  layer  and  A  a  constant  if  Beer's  law  holds.  Strictly 
speaking,  the  above  equation  holds  for  monochromatic  light.  For  ordi- 
nary white  light  we  would  have  to  integrate  this  equation  over  the  range 
of  wave-lengths  used.  The  equation  would  then  have  the  form 


r 

=  Jo/     ePW 

J  A, 


The  quantity  /?  is  called  the  index  of  absorption  and  A  the  molecular  extinc- 
tion coefficient.    If  the  absorption  is  proportionately  greater  in  the  more 
concentrated  solutions,  then  Beer's  law  fails 
and  A    decreases   inversely  as   the   concen- 


509 
521 
536 


Potassium  dichromate. 


Value  of  A. 


62.4 
28.7 
7.24 


Value  of  A. 


58.0 

26.2 

6.2 


tration. 


From  photometric  measurements  Sette- 
gast1  and  Sabatier2  conclude  that  the  absorp- 
tion spectrum  of  potassium  dichromate  is 
the  same  as  that  of  chromic  acid,  and  that 
the  absorption  spectrum  of  potassium  chro- 
mate is  entirely  different.  This  is  corrobo- 
rated by  the  present  work.  Settegast  finds 

that  Beer's  law  does  not  hold  for  potassium  chromate  and  potassium 
dichromate,  the  coefficient  A  decreasing  with  increasing  concentration. 
Griinbaum 3  finds  the  accompanying  values  of  A  and  e  where  e  =  c/A . 

1  Wied.  Ann.,  7,  242-271  (1879). 
3  Compt.  rend.,  103,  49-52  (1886). 
1  Ann.  Phys.,  12,  1004,  1011  (1903). 


POTASSIUM   SALTS. 


25 


It  will  be  seen  that  the  deviation  here  from  Beer's  law  is  in  the  opposite 
direction  from  that  found  by  Settegast.  Griinbaum  finds  that  e  and  there- 
fore A  depend  on  the  depth  of  layer. 

An  example  will  be  given  where  the  same  concentration  and  different 
depths  of  the  solution  were  used: 


A. 

Value  of  <  for  c-0.0034. 

25  cm.  layer. 

12  cm.  layer. 

5  cm.  layer. 

521 
521 

0.0758 
.0761 

0.0818 
.0830 

0.0884 
.0897 

Our  work  indicates  that  Beer's  law  holds  for  all  dilute  solutions,  and 
usually  the  deviations  for  concentrated  solutions  are  very  small.  Of 
the  potassium  salts  above  described,  only  potassium  chromate  between  2 
normal  and  0.25  normal  showed  any  considerable  deviation  from  Beer's 
law,  and  in  this  case  the  absorption  of  the  concentrated  solution  was  greater 
by  about  40  Angstrom  units  than  would  be  expected  if  Beer's  law  held. 

The  present  method  is  a  very  good  qualitative  test  of  Beer's  law,  and 
gives  the  results  for  each  wave-length,  whereas  most  photometric  methods 
only  give  integrated  results  over  a  more  or  less  wide  region  of  wave-length. 
A  very  good  review  of  the  work  upon  Beer's  law  has  been  published  by 
G.  Rudorf.1  A  more  detailed  account  of  the  work  upon  the  potassium  salts 
will  now  be  given. 

POTASSIUM  CHBOMATB. 

Potassium  chromate  (K2CrO4)  (Plates  1  and  2)  was  mapped  for 
ranges  of  concentration  between  2  normal  and  0.00049  normal  concentra- 
tion. In  every  case  the  length  of  exposure  to  the  Nernst  glower  was  {|Q} 
seconds,  the  current  being  0.8  ampere,  and  when  there  was  transmission  in 
the  ultra-violet,  the  length  of  exposure  to  the  spark  was  2  minutes.  The 
slit-width  was  0.08  mm.  and  the  depth  of  cell  in  each  case  was  3  mm.  The 
following  table  gives  the  limits  of  absorption  bands.  The  limit  is  usually 
taken  as  midway  between  complete  transmission  and  complete  absorption. 
For  the  more  concentrated  solutions  the  region  between  complete  absorption 
and  transmission  was  quite  narrow,  not  being  more  than  20  or  30  Angstrom 
units.  For  the  more  dilute  solutions  the  edges  of  the  bands  were  much 
more  diffuse. 

This  work  here  also  (Plates  3  and  4)  indicates  that  Beer's  law  holds  for 
all  dilute  solutions  which  have  thus  far  been  tested,  and  usually  the  devia- 
tions from  Beer's  law  for  concentrated  solutions  is  small.  The  present 
method  is  very  crude  as  far  as  dealing  with  relative  intensities.  In  some 
cases,  however,  it  is  quite  sensitive,  although  it  never  gives  absolute  values 
for  A.  As  an  example,  we  will  take  that  of  potassium  chromate  between 
concentrations  2  normal  and  0.25  normal.  When  the  depth  of  cell  is  kept 
constant  at  3  mm.,  the  position  of  the  edge  of  transmission  for  the  2  normal 
solution  is  >l  4970,  for  the  0.25  normal  solution  X  4750.  In  the  run  for  Beer's 
law  (where  cl  is  kept  constant)  it  is  found  that  the  absorption  is  about  40 

>  Jahrb.  Rad.  u.  Elek.,  3,  422  (1906);  and  4,  380  (1907). 


26 


A    STUDY    OF   THE    ABSORPTION   SPECTRA. 


Angstrdm  units  nearer  the  violet  for  the  most  concentrated  solution,  com- 
pared with  the  0.025  normal  solution.  This  would  mean  that  the  value  of 
A  had  increased  with  increase  in  concentration.  On  account  of  the  sharp- 
ness of  the  edge  of  absorption  it  is  possible  to  detect  a  change  in  the  edge 


Concentration. 

Edge  of 
short  wave-length 
absorption. 

Edges  of  violet  trans- 
mission band. 

Concentration. 

Edge  of  violet 
transmission  band. 

0.00049 

A  3820 

A  3600 

0.03125 

A  4500 

.00065 

A  3870 

A  3500        A  2700 

.042 

,14520 

.0009 

,13900 

A  3450        A  2800 

.058 

A  4570 

.0013 

,13970 

A  3400        A  2900 

.083 

A  4640 

.0019 

,14000 

X  3350        X  2940 

.125 

A  4720 

.0029 

A  4050 

A  3300        A  2960 

.19 

A  4750 

.0039 

A  4100 

A  3240        A  3000 

.25 

A  4800 

.0052 

X  4200 

A  3180        A  3040 

.33 

A  4840 

.007 

A  4250 

A  3150        X  3070 

.47 

A  4880 

.0104 

,14350 

A  3140        ,13100 

.66 

A  4920 

.015 

A  4400 

1.0 

A  4960 

.024 

A  4450 

1.5 

A  4970 

.03125 

,14500 

2.0 

of  10  Angstrom  units,  and  this  would  correspond  to  a  change  in  A  of  about 
20  per  cent.  One  of  the  larger  errors  entering  into  the  determination  ia 
getting  the  depth  of  layer  correct  for  their  smallest  values.  The  method 
is  very  useful  in  showing  the  results  over  the  whole  spectrum. 

POTASSIUM  BICHROMATE. 

The  spectrograms  showing  the  variation  of  absorption  of  potassium 
dichromate  in  water,  keeping  the  depth  of  layer  constant  and  changing  the 
concentration,  are  Plate  5,  B,  and  Plate  6,  A,  B.  The  absorption  is  much 
greater  than  for  potassium  chromate  and  the  limits  of  the  bands  are  much 
more  diffuse.  The  change  of  the  absorption  with  change  in  concentration  is 
much  greater  than  for  potassium  chromate. 

The  concentrations  for  B,  Plate  5  are,  beginning  with  the  strip  next 
to  the  scale,  0.333,  0.25,  0.16,  0.11,  0.083,  0.055,  and  0.042  normal;  the 
depth  of  layer  being  3  mm.  The  distance  between  complete  absorption 
and  complete  transmission  is  about  70  Angstrom  units  for  the  0.3  normal 
solution  and  over  200  Angstrom  units  for  the  0.04  normal  solution.  The 
limits  of  the  absorption  band  beginning  with  the  most  concentrated  solu- 
tion are  U  5340,  5320,  5300,  5240,  5200,  5140,  and  5100. 

For  Plate  6,  A,  the  concentrations  are  0.042,  0.031,  0.021,  0.014, 
0.0104,  0.0068,  and  0.0052  normal,  beginning  with  the  strip  next  the  scale. 
The  depth  of  layer  is  3  mm.  In  this  case  the  edge  of  the  absorption  is  very 
diffuse,  the  distance  between  complete  absorption  and  transmission  being 
over  200  Angstrdm  units.  The  limits  of  the  band  for  the  various  concentra- 
tions are  U  5100,  4900,  4800,  4700,  4500,  4300,  and  4200,  approximately. 

The  concentrations  for  Plate  6,  B,  are  0.0052,  0.0039,  0.0026,  0.0017, 
0.00087,  and  0.00065  normal,  starting  with  the  strip  nearest  the  scale. 
The  limits  of  the  red  side  of  the  absorption  band  are  roughly  U  4200,  4150, 
4050,  4000,  3900.  The  violet  edge  of  this  absorption  band  makes  its 


POTASSIUM   SALTS.  27 

appearance  at  the  concentration  0.0026  normal,  and  has  a  limit  at  about 
I  3200.  For  0.0017  normal  the  limit  is  3300,  and  for  0.00087  normal, 
/I  3400.  The  middle  of  this  absorption  band  for  O.OOOS7  normal  would 
thus  be  about  -1  3800.  The  ultra-violet  band  which  appears  at  0.0017 
normal  has  limits  upon  its  red  side  of  X  3100;  for  0.00087  normal,  A  3000; 
and  0.00065  normal,  X  2900. 

Plate  5,  A,  tests  Beer's  law.  Starting  with  the  strip  nearest  the 
numbered  scale  the  concentrations  are  0.33,  0.25,  0.16,  0.11,  0.083,  0.055, 
and  0.042  normal;  the  corresponding  depths  of  cell  being  3,  4,  6,  9,  13, 
18,  and  24  mm.  The  limit  of  absorption  is  at  >l  5350.  Beer's  law  is  found 
to  hold. 

Plate  7,  A,  and  B,  contains  spectrograms  in  which  Beer's  law  is  tested 
for  more  dilute  solutions.  The  concentrations  and  depths  of  cell  are  given 
in  the  general  description  of  the  plates.  In  A  the  limit  of  absorption  is  at 
>l  5000,  in  B  at  A  4200.  In  both  cases  Beer's  law  holds.  The  edge  of  the 
absorption  band  in  this  case  is  quite  broad. 

POTASSIUM  FERKOCYANIDB  IN  WATER. 

Potassium  ferrocyanide  has  a  color  very  similar  to  that  of  potassium 
ferricyanide.  It  is  practically  insoluble  in  all  solvents  except  water.  Its 
spectrum  has  been  mapped  out  for  concentrations  ranging  from  0.5  to 
0.00078  normal,  and  Beer's  law  has  also  been  tested  between  these  limits. 

The  methods  of  exposure  have  been  the  same  in  all  the  spectrograms 
taken  of  the  potassium  salts.  The  time  of  exposure  to  the  Nernst  glower 
was  80  seconds,  the  current  being  0.8  ampere  and  the  slit  width  0.08  mm. 
When  there  was  any  transmission  in  the  ultra-violet,  exposure  was  made 
for  120  seconds  to  the  spark. 

The  mapping  of  the  spectrum  was  done  by  keeping  the  depth  of  cell 
constant  at  3  mm.  and  gradually  changing  the  concentration  of  the  solution. 
Plate  8,  A  and  B,  shows  the  variation  of  the  absorption  of  light  with  varia- 
tion in  the  concentration.  Starting  with  the  strip  at  the  top  of  A,  the  con- 
centrations were  0.5,  0.375,  0.25,  0.17,  0.117,  0.083,  and  0.062  normal. 
The  corresponding  limits  of  absorption  were  U  3950,  3920,  3890,  3840,  3790, 
3750,  and  3700.  The  region  between  complete  transmission  and  complete 
absorption  was  quite  wide,  being  almost  100  Angstrom  units.  This  is  in 
marked  contrast  with  the  sharp  edge  of  the  absorption  band  for  concen- 
trated solutions  of  potassium  ferricyanide. 

Starting  with  the  upper  strip  of  spectrogram  B,  the  concentrations 
were  0.0625,  0.0469,  0.0312,  0.0208,  0.0144,  0.0103,  and  0.0078  normal. 

The  corresponding  limits  of  absorption  in  this  case  were  M  3700,  3640, 
3600,  3500,  3400,  3300  and  3150.  For  dilutions  greater  than  this  there  is 
almost  complete  transmission  throughout  the  whole  violet  region. 

Two  spectrograms  (Plate  9,  A  and  B)  are  given  to  show  that  Beer's 
law  holds  for  solution  of  potassium  ferrocyanide.  Starting  with  the  upper 
strip  of  A,  the  concentrations  were  0.5,  0.375,  0.25,  0.17,  0.117,  0.083, 
and  0.062  normal.  The  corresponding  concentrations  in  spectrogram  B 
were  0.0625,  0.0469,  0.0312,  0.021,  0.0144,  0.0103,  and  0.0078  normal. 
The  depths  of  layer  starting  at  the  top  of  either  A  or  B  were  3,  4,  6,  9,  13,  18, 


28  A    STUDY   OF   THE    ABSORPTION  SPECTRA. 

and  24  mm.    From  the  spectrograms  we  see  that  Beer's  law  holds  within 
the  range  of  concentrations  studied. 

The  above  spectrograms  show  that  the  absorption  spectra  of  potassium 
ferricyanide  and  of  potassium  ferrocyanide  are  quite  different.  This  differ- 
ence is  shown  in  three  ways:  First,  for  the  same  concentrations  the  absorp- 
tion of  potassium  ferricyanide  is  much  the  greater;  second,  the  limit  of  the 
absorption  band  of  the  ferricyanide  is  much  sharper;  and  third,  for  certain 
concentrations  of  the  potassium  ferricyanide  solution,  there  appears  a  blue- 
violet  band  having  its  center  at  about  A  4200.  The  band  is  entirely  absent 
in  the  absorption  of  potassium  ferrocyanide. 

POTASSIUM  FERRICYANIDE  IN  WATER. 

Potassium  ferricyanide,  KsFe(CN)6,  usually  exists  in  the  form  of  dark- 
red  anhydrous  monoclinic  prisms.  It  dissolves  in  water,  giving  a  yellowish 
solution,  which  on  dilution  becomes  lemon-yellow  in  color.  According  to 
Locke  and  Edwards  1  an  isomeric  form  of  potassium  ferricyanide  exists  as 
olive-colored  crystals  having  the  composition  K3Fe(CN)6,H2O. 

Potassium  ferricyanide  is  but  slightly  soluble  in  solvents  other  than 
water,  and  for  this  reason  the  present  work  was  limited  to  aqueous  solutions. 

One  reason  for  examining  the  absorption  spectra  of  potassium  ferri- 
cyanide and  potassium  ferrocyanide  was  to  find  a  clue,  if  possible,  to  the 
manner  in  which  these  solutions  dissociated  in  dilute  aqueous  solutions. 
Most  physical  chemical  investigators  have  considered  that  these  two  salts 
dissociate  according  to  the  following  equations: 


K3FeC,N8    <=>    K,  K,  K,  FeC6N8    and 


K4FeCeN.    <=±    K,  K,  K,  K,  FeC.N. 

The  absorption  spectra  of  these  two  salts  would  then  be  due  to  one 
or  more  of  the  four  kinds  of  absorbers,  K3FeC6N6,  FeC6Ne,  K4FeC6N6,  and 
FeC6N6,  and  it  is  quite  probable  that  each  one  of  these  absorbers  would 
give  rise  to  a  different  absorption  spectrum. 

According  to  Jones  and  Getman,  and  Jones  and  Bassett  (Hydrates  in 
Aqueous  Solution,  p.  46,  Carnegie  Institution  of  Washington  Publication 
No.  60),  it  is  possible  that  the  dissociation  takes  place  in  a  different 
manner.  They  concluded  from  conductivity  measurements  that  potassium 
ferricyanide  and  potassium  ferrocyanide  dissociate  as  follows: 


K,FeC6Na    *±    K,  CN,  K,  ON,  K,  FeC4N4    and 


K4FeC6N6  *±  K,  CN,  K,  CN,  K,  CN,  K,  FeC3N3 
The  absorbers  in  an  aqueous  solution  in  this  case  would  include  four 
groups,  K3FeC6N6,  FeC4N4,  K4FeC,Ne,  nd  FeC3Ns.  Thus,  according  to  either 
theory  we  get  four  kinds  of  absorbers.  If  we  found  that  we  had  four 
different  kinds  of  absorbers  in  potassium  ferricyanide  and  potassium  ferro- 
cyanide solutions  and  mapped  these  spectra,  and  if  we  knew  the  absorption 

1  Amer.  Chem.  Journ.,  21,  193  (1899). 


POTASSIUM   SALTS.  29 


spectra  of  either  FeC6N6,  FeC6N8,  FeC4N4,  or  FeC3N3,  then  we  could  tell 
whether  the  salts  dissociated  according  to  the  first  or  the  second  theory,  or 
according  to  some  other  method.  But  as  we  have  thus  far  investigated 
only  the  absorption  spectra  of  potassium  ferricyanide  and  potassium  ferro- 
cyanide,  no  conclusion  as  to  the  manner  of  dissociation  could  be  drawn. 

It  would  be  interesting  in  this  connection  to  study  potassium  ferro- 
cyanide  carbonyl,  K3FeC5N5CO:3iH2O,  ferrocyanhydric  acid,  H4FeC6N6, 
and  ferricyanhydric  acid,  H3FeC3N3.  Both  ferrocyanhydric  acid  and 
ferricyanhydric  acid  are  soluble  in  water  and  alcohol. 

The  absorption  spectra  of  a  3-mm.  depth  of  cell  of  potassium  ferri- 
cyanide in  water  were  photographed  between  concentrations  1  normal  and 
0.00024  normal,  and  are  given  in  Plates  10  and  11.  The  conditions  of 
exposure  in  these  two  plates  were  the  same,  80  seconds  to  the  Nernst  glower 
for  the  visible  portion  of  the  spectrum  and  2  minutes  to  the  spark  for  the 
ultra-violet  region.  The  current  through  the  Nernst  glower  was  kept 
constant  at  0.8  ampere.  The  slit-width  was  0.08  mm. 

Potassium  ferricyanide  has  a  very  simple  absorption  spectrum.  For  the 
concentrated  solutions  all  the  short  wave-lengths  beyond  the  green  are 
absorbed.  As  the  concentration  is  decreased  the  limit  of  absorption  grad- 
ually recedes  towards  the  ultra-violet.  The  region  between  complete  trans- 
mission and  complete  absorption  is  quite  narrow  for  the  more  concentrated 
solutions,  and  for  this  reason  solutions  of  potassium  ferricyanide  could  be 
used  as  light-screens.  The  concentrations  starting  at  the  top  of  A,  Plate  10 
are  1,  0.75,  0.50,  0.333,  0.231,  0.166,  and  0.125  normal,  the  corresponding 
limits  of  absorption  being  U  4800,  4780,  4765,  4730,  4710,  4680,  and  4650. 
The  distance  between  complete  absorption  and  complete  transmission  as 
measured  on  the  spectrum  photograph  was  not  greater  than  40  Angstrom 
units. 

The  concentrations  starting  at  the  top  of  B,  Plate  10  are  0.125, 
0.0937,  0.0625,  0.0417,  0.029,  0.0208,  and  0.0156  normal.  The  correspond- 
ing limits  of  absorption  are  M  4650,  4630,  4620,  4600,  4560,  4520,  and  4500. 
As  the  concentration  becomes  small  the  limit  of  absorption  becomes  more 
and  more  diffuse.  For  the  0.0156  normal  concentration  the  distance  between 
complete  transmission  and  complete  absorption  was  almost  100  Angstrom 
units.  For  about  this  concentration  a  faint  transmission  band  begins  to 
appear  in  the  ultra-violet. 

The  concentrations  starting  at  the  top  of  A,  Plate  11  are  0.0156, 
0.0117,  0.0078,  0.0052,  0.0036,  0.0026,  and  0.00195  normal.  In  this  spec- 
trogram two  bands  of  absorption  appear,  a  blue-violet  band  and  an  ultra- 
violet band.  For  the  0.0156  normal  solution  the  blue-violet  absorption 
band  is  bounded  by  X  4500  and  A  3570,  for  0.0117  normal  by  U  4450  and 
3580,  for  0.0078  normal  U  4400  and  4000.  The  middle  of  the  band  at  its 
origin  is  about  A  4200.  The  long  wave-length  edge  of  the  ultra-violet  band 
has  the  following  positions,  for  normal  0.0156,  A  3550;  0.0117,  I  3500; 
0.0078,  A  3300;  0.0052,  A  3250;  and  0.0036,  A  3150.  For  concentrations 
less  than  this  there  is  more  or  less  general  transmission  throughout  the 
ultra-violet  region. 


30  A    STUDY   OP   THE    ABSORPTION  SPECTRA. 

The  concentrations  for  B,  Plate  11,  starting  with  the  strip  nearest  the 
top,  were  0.00195,  0.00146, 0.00098, 0.00065,  0.00045,  0.00037,  and  0.000244 
normal.  In  this  spectrogram  there  is  somewhat  general  transmission 
throughout  the  whole  ultra-violet  region.  In  the  ultra-violet  there  appear 
three  weak  bands  that  do  not  seem  to  be  due  to  any  feeble  intensity  of  the 
spark-spectra  in  these  regions.  The  positions  of  these  bands  are  ^  2500 
to  2600,  ^  2950  to  3050,  and  >l  3200  to  3250. 

Spectrograms  were  made  to  test  Beer's  law  between  concentrations 
1  and  0.000244  normal,  four  spectrograms  being  made  in  all.  In  each  one 
of  these  spectrograms  the  amount  of  absorbing  salt  in  the  solution  through 
which  the  light  passed,  times  the  length  of  the  solution  was  constant. 
Under  these  conditions  if  Beer's  law  holds  the  absorption  spectra  in  each 
strip  will  be  the  same. 

Plate  12,  A  represents  a  spectrogram  showing  that  Beer's  law  holds 
for  a  potassium  ferricyanide  solution  between  concentrations  1  and 
0.125  normal.  Starting  with  the  strip  at  the  top  the  concentrations  were 
1,  0.75,  0.50,  0.333,  0.231,  0.166,  and  0.125  normal.  The  depths  of  cell 
were  3,  4,  6,  9,  13,  18,  and  24  mm.,  respectively.  The  exposure  to  the 
Nernst  glower  was  made  for  80  seconds,  slit-width  being  0.08  mm.  and  the 
current  0.8  ampere.  The  limit  of  absorption  for  each  strip  is  ^  4800.  B, 
Plate  12,  was  taken  under  the  same  conditions  as  A,  each  strip,  however, 
being  exposed  to  the  spark  for  3  minutes.  The  concentrations  for  B,  start- 
ing with  the  upper  strip,  were  0.125,  0.094,  0.0625,  0.0417,  0.029,  0.0208, 
and  0.0156  normal,  the  depths  of  cell  being  3,  4,  6,  9,  13,  18,  and  24  mm. 
In  this  case  also  Beer's  law  held  to  within  the  limits  of  error  of  this  method. 

Spectrograms  not  published  were  made  in  a  similar  way  for  concentra- 
tions 0.0156,  0.0117,  0.0078,  0.0052,  0.0036,  0.0026,  and  0.00195  normal; 
also  for  concentrations  0.00195,0.00146.  0.00098,  0.00065,  0.00045,  0.00037, 
and  0.000244  normal,  the  depths  of  cell  being  3,  4,  6,  9,  13,  18,  and  24  mm., 
respectively.  In  all  these  cases  Beer's  law  holds. 

A  question  that  is  sometimes  asked  is,  What  is  the  sensitiveness  of  this 
method  to  small  changes  in  concentration  ?  This  depends  of  course  on  the 
absolute  concentration  itself.  For  concentrated  solutions  of  potassium 
ferricyanide  it  is  possible  to  detect  a  change  in  the  edge  of  the  absorption 
to  within  10  Angstrom  units.  For  concentrations  of  0.125  normal,  then,  it 
would  be  possible  to  detect  changes  of  concentration  of  less  than  normal 
0.02.  It  will  be  noticed  that  the  relative  sensibility  to  change  in  concentra- 
tion is  not  very  great,  but  for  dilute  solutions  the  absolute  sensibility  is 
much  greater.  One  reason  for  this  is  that  errors  in  the  depth  of  cell  for  a 
considerable  cell-depth  are  small  as  compared  with  the  depth  of  cell  itself. 


CHAPTER  IV. 

COBALT  SALTS. 

Review  of  previous  work. — Cobalt  chloride  and  bromide  in  glycerol. — Effect  of 
rise  in  temperature  on  aqueous  solutions  of  cobalt  chloride,  cobalt  nitrate,  cobalt 
sulphate,  cobalt  acetate,  and  cobalt  sulphocyanate. — Effect  of  rise  in  tempera- 
ture on  the  absorption  spectra  of  aqueous  solutions  of  mixtures  of  cobalt 
chloride  and  aluminium  chloride,  and  of  cobalt  chloride  and  calcium  chloride. 
Conductivity  data. — Summary. 

REVIEW  OF  PREVIOUS  WORK. 

Some  of  the  most  beautiful  color-changes  known  are  those  shown  by 
solutions  of  cobalt  and  copper  salts.  For  example,  aqueous  solutions  of 
cobalt  chloride  are  purplish  red  in  color.  When  a  concentrated  aqueous 
solution  of  cobalt  chloride  is  heated,  or  treated  with  hydrochloric  acid, 
aluminium  chloride,  or  calcium  chloride,  its  color  changes  to  blue,  the  change 
being  quite  sudden  under  certain  conditions.  On  the  other  hand,  the  addi- 
tion of  zinc  and  mercury  chlorides  produces  the  reverse  effect,  changing 
the  blue  solution  into  a  red  one.  Similar  changes  result  when  cobalt  salts 
dissolved  in  other  solvents  are  treated  in  the  same  way  as  aqueous  solutions. 
A  very  considerable  amount  of  work  has  been  done  by  various  workers  and 
in  general  different  theories  have  been  offered  to  explain  the  results. 

Russel,1  Potilitzin,2  Lescoeur,3  Etard,4  and  others  favored  the  view 
that  these  color-changes  were  due  to  the  formation  of  different  compounds 
of  the  cobalt  salt  with  the  solvent.  The  hexahydrate  CoCl2.6H20  is  red, 
and  when  heated  it  is  changed  into  the  reddish  lilac  dihydrate  CoCl2.2H2O. 
When  the  latter  compound  is  heated  it  is  transformed  into  the  dark-violet 
monohydrate,  CoCl2.H20.  The  anhydrous  salt  is  blue  and  is  formed  at 
about  140°  C.  Etard  showed  that  the  solubility  curve  changed  in  direction 
at  the  same  temperature  that  the  red  solution  becomes  blue.  Charpy ' 
showed  the  same  to  be  true  for  the  vapor-tension  temperature  curve. 

Engel,"  Donnan  and  Bassett,7  Donnan,8  Moore,"  and  others  do  not 
believe  that  these  color-changes  are  solvation  effects  at  all.  Engel  considers 
that  double  haloid  salts  may  be  formed.  He  points  out  the  fact  that  the 
blue  anhydrous  cobalt  chloride  becomes  red  when  sufficiently  cooled,  and 
that  the  red  anhydrous  sulphate  becomes  violet  when  heated.  Donnan 
and  Bassett  consider  that  the  blue  color  of  cobalt  salts  is  due  to  the  forma- 
tion of  complex  anions  containing  cobalt.  By  boiling-point  determinations 

1  Proc.  Roy.  Soc.,  32,  258  (1881);  Chem.  News,  59, 93  (1889). 

1  Bull.  Soc.  Chem.  (3),  6,  264  (1891);  Ber.  d.  deutsch.  chem.  Gesell.,  17,  276  (1884). 

» Ann.  Chim.  Phys.  (6),  19,  547  (1890). 

«Compt.  rend.,  113,  699  (1891). 

tlbid.,  113,  794  (1901). 

•  Bull.  Soc.  Chim.  (3),  5,  460  (1901). 
» Journ.  Chem.  Soc.,  81,  942  (1902). 

•  Versuche  wber  der  Beziehung  zwischen  der  elektrolytischen  Dissoziation  und  der  Licht- 

absorption  in  Losungen.  Zeit.  phys.  Chem.,  19, 465-488  (1896) ;  S3,  317-320  (1905). 

•  Phys.  Rev.,  23,  No.  4,  p.  321,  357  (1906). 

31 


32  A   STUDY   OF   THE   ABSORPTION  SPECTRA. 

they  concluded  that  mercuric  and  cobalt  chlorides  in  solution  form  com- 
pounds. When  metallic  ions  of  relatively  strong  basic  properties  like  the 
alkaline  earths  or  hydrogen  are  introduced  with  chlorine  ions  into  a  cobalt 
chloride  solution,  there  is  a  greater  formation  of  complex  cobalt  anions 
similar  to  that  given  by  the  following  equation. 


CoCl3  +  2Gl    ?±    CoCl4  CoCl3+Cl    <±    CoCls 

On  the  other  hand,  Zn,  Cd,  Hg,  Sb,  Sn,  etc.,  form  negative  complexes 
easier  than  cobalt  and  hence  they  will  cause  the  cobalt  complexes  to  break 
up. 

CoCl4    +±    CoCl2  +  2Cl  ZnCl2+2Cl    <=±    ZnCl4 

Vaillant  :  has  made  a  quantitative  comparison  between  dissociation 
and  light  absorption.  In  general  there  is  a  close  parallelism  between  these 
two  phenomena.  For  concentrated  solutions,  however,  there  are  marked 
differences  which  suggest  other  products,  and  these  Vaillant  called  hydrates. 
Pfliiger,2  Vaillant  and  Moore3  have  studied  various  salt  solutions  photo- 
metrically. They  find  the  same  absorption  coefficients  for  dilute  solutions 
of  sodium,  potassium,  and  barium  permanganates,  but  for  concentrated 
solutions  they  find  differences.  They  conclude  that  absorption  depends 
upon  ionization. 

A  very  detailed  study  has  been  made  by  Hartley  4  of  the  effect  of  tem- 
perature on  the  absorption  spectra  of  solutions.  Hartley  considered  that 
the  effect  of  change  in  temperature  was  largely  due  to  change  in  the  solva- 
tion  of  the  dissolved  salt.  Bois  and  Elias  5  studied  cobaltammonium- 
rhodamid  at  18°  and  —  190°  C.  At  the  lower  temperature  the  bands 
were  smaller  but  were  still  very  diffuse. 

Uhler6  has  studied  cobalt  salts  very  systematically.  Cobalt  chloride 
in  water  was  found  to  show  rather  fine  bands  at  X  6970,  >l  6610,  ^  6400  (weak), 
A  6245  (weak),  and  >l  6095  (weak).  In  ethyl  alcohol  bands  were  found  at 
>l  6950,  X  6360,  ^  6150,  and  /I  6000. 

Jones  and  Anderson  7  have  made  a  detailed  study  of  cobalt  salts. 
Solutions  of  all  the  salts  studied,  except  the  sulphate,  have  a  region  of  ultra- 
violet one-sided  absorption.  This  they  consider  as  due  to  association  or 
solvation.  In  addition  to  the  one-sided  ultra-violet  band,  cobalt  chloride 
has  a  band  at  ^  3300  which  disappears  very  rapidly  with  dilution.  This 
band  they  believe  is  due  to  some  simple  hydrate,  and  they  consider  that 
this  simple  hydrate  is  only  stable  in  very  concentrated  solutions  or  at  high 
temperatures.  The  green  band  appears  for  all  aqueous  solutions,  and  is 
independent  of  whether  the  cobalt  exists  as  an  ion,  molecule,  as  an  aggre- 
gate, or  as  a  solvate;  the  absorbing  power  being  apparently  due  to  the  cobalt 

1  Ann.  Chim.  Phys.  (7),  28,  213  (1903). 

2  Ann.  Phys.  (4),  12,  1903. 

3  Loc.  cit. 

4  Dub.  Trans.  (2),  7,  253,  312  (1900). 
•Ann.  Phys.,  12,  262  (1908). 

*  Hydrates  in  Aqueous  Solution,  Carnegie  Institution  of  Washington  Pub.  No.  60. 
7  The  Absorption  Spectra  of  Solutions,  Carnegie  Institution  of  Washington  Pub. 

NO.  no: 


COBALT    SALTS. 


33 


atom.  Absorption  in  the  red  is  considered  to  be  due  to  a  simple  solvate. 
In  alcohol  cobalt  chloride  has  bands  at  A  3100  and  A  3600,  and  also  a  green 
band.  In  methyl  alcohol  they  find  a  fairly  narrow  band  at  A  5910,  one  at 
X  6050;  a  narrow  intense  band  at  >l  6240;  a  wide  band  at  /I  6450,  and  a  wide 
intense  band  at  A  6700.  The  position  and  relative  intensity  of  these  bands 
are  very  different  from  that  of  the  cobalt  chloride  water-bands  described  by 
Uhler.  In  acetone  broad  bands  appear  at  >l  5725,  /I  6200,  and  A  6780.  These 
do  not  appear  to  be  broken  up  into  sharper  bands  under  any  conditions. 
By  the  addition  of  5  per  cent  of  water  to  an  ethyl  alcohol  solution  of  cobalt 
chloride,  the  water-bands  are  made  to  appear,  while  for  an  acetone  solution 
it  requires  the  presence  of  at  least  10  per  cent  of  water  to  bring  out  the 
water-bands.  Cobalt  and  calcium  bromides  in  water  are  found  to  give 
bands  at  A  6400,  A  6650,  and  X  6950.  Cobalt  bromide  in  acetone  has  bands 
in  the  red  that  differ  quite  markedly  from  those  of  cobalt  chloride  in  acetone. 


Cobalt  chloride  in 
water  (BShlendorf). 

CoCh  in  alcohol 
(Bohlendorf). 

Cobalt  chlorate  in 
alcohol  (Fonnanek). 

A  7100  to  6880 

A  7100  to  6570 

A  6850  to  6320 

A  6750  to  6530 

A  6400 

A  6400 

A  6260  to  6170 

A  6250  to  6170 

A  6245 

/I  6070 

/I  6070 

A  6058 

A  5610  to  4980 

.... 

A  5906 

A  5720 

A  5265 

A  5120 

Rizzo  l  has  investigated  the  effect  of  rise  in  temperature  on  the  absorp- 
tion bands  of  cobalt  glass.     He  gives  the  following  figures: 


15°. 

300°. 

500°. 

A  6870  to  A  6380 
A  6030  to  A  5780 
A  5520 

A  6900  to  A  6480 
A  61  10  to  A  5800 
A  5630 

A  6920  to  A  6460 
A  6130  to  A  5800 
A  5650 

From  the  above  summary  it  will  be  seen  that  our  knowledge  of  the  red 
cobalt  bands  is  very  small  at  present.  Much  more  work,  similar  to  that 
to  be  described  on  the  uranyl  bands,  remains  to  be  done.  Apparently 
these  cobalt  bands  are  somewhat  different  from  the  uranyl  bands;  at  any 
rate,  the  bands  investigated  by  Bois  and  Elias  did  not  break  up  into  fine, 
sharp  bands  at  very  low  temperatures. 

In  discussing  the  various  spectrograms  that  show  the  effect  of  change 
in  temperature  on  the  absorption  spectra  of  salts,  these  spectra  will  be 
divided  into  three  kinds: 

The  first  kind  of  absorption  consists  of  wide  bands,  in  many  cases 
hundreds  of  Angstrom  units  wide.  In  many  of  the  spectrograms  only 
one  edge  of  the  band  may  appear,  the  other  edge  of  it  lying  in  parts  of  the 
spectrum  to  which  the  photographic  film  is  not  sensitive,  or  to  which  the 


1  Atti  di  Torino,  26,  632-638  (1891). 


34  A   STUDY   OP  THE  ABSORPTION  SPECTRA. 

spectroscopic  apparatus  is  not  properly  adapted.  Examples  of  this  kind 
of  absorption  are  given  by  the  copper  or  nickel  salts,  the  ferricyanides, 
the  chromates,  etc.  There  is  not  the  slightest  indication  of  a  finer  structure 
to  these  bands. 

The  second  kind  of  absorption  spectra  consists  of  diffuse  bands  that 
are  quite  narrow  in  many  cases  and  are  usually  very  weak  at  ordinary 
temperatures.  These  bands  may  be  from  10  to  several  hundred  Angstrom 
units  wide,  and  at  very  low  temperatures  may  be  broken  up  into  finer  and 
sharper  bands.  Examples  of  this  kind  of  bands  are  the  cobalt,  uranyl,  or 
uranous  bands.  In  many  cases  these  bands  appear  only  under  very  special 
conditions  of  concentration  and  depth  of  cell.  If  the  amount  of  absorbing 
material  is  large  there  is  usually  a  wide  absorption  band  in  the  region. 
This  is  well  illustrated  by  the  uranyl  bands  and  the  blue-violet  band  of  the 
uranyl  salts.  If  the  amount  of  absorbing  material  is  small  the  transmission 
of  light  is  so  great  that  these  faint  bands  are  entirely  obliterated. 

The  third  class  of  bands  are  sharp  and  appear  over  rather  wide  ranges 
of  concentration.  They  are  exemplified  by  the  neodymium  and  erbium 
bands.  This  classification  of  bands  is  quite  adequate  for  the  present  article 
on  account  of  the  salts  studied  and  the  temperatures  used.  It  is  very 
probable,  however,  that  the  latter  two  kinds  of  bands  gradually  merge  into 
each  other. 

GLYCEROL  SOLUTIONS  OP  COBALT  SALTS. 

A  dilute  solution  of  cobalt  chloride  was  placed  in  the  silica  cell  and 
exposures  were  made  at  10°,  100°,  and  200°  C.  At  10°  and  100°  there  was 
practically  complete  transmission  throughout  the  visible  portion  of  the 
spectrum.  At  200°  the  whole  shorter  wave-length  portion  of  the  spectrum 
was  absorbed  up  to  X  6200.  No  indications  of  any  fine  bands  in  the  red 
were  to  be  noticed.  A  solution  of  normal  cobalt  bromide  in  glycerol  was 
exposed  in  the  same  way  as  the  chloride,  with  practically  no  change  in  the 
absorption  with  rise  in  temperature.  A  more  concentrated  solution  of 
cobalt  bromide  in  glycerol  was  exposed  in  the  silica  cell  at  10°,  100°,  and 
200°.  At  10°  there  was  a  very  diffuse  absorption  band  extending  from 
A  5000  to  A  5300.  At  100°  this  band  had  broadened  so  as  to  reach  from 
^  4900  to  A  5400.  At  200°  the  whole  of  the  spectrum  of  wave-length  less 
than  X  6200  was  absorbed.  No  signs  of  the  red  bands  appeared.  Concen- 
trated solutions  of  cobalt  salts  in  glycerol  become  blue  on  being  heated. 
Unfortunately  the  length  of  the  silica  cell  prevented  the  use  of  concentrated 
solutions. 

AQUEOUS  SOLUTIONS  OF  COBALT  SALTS. 

A  spectrogram,  Plate  13,  A,  of  the  absorption  spectrum  of  an  aqueous 
solution  of  cobalt  chloride  was  made  for  a  2.37  normal  concentration  and  a 
depth  of  cell  of  1.3  mm.  The  current  in  the  Nernst  glower  was  0.7  ampere, 
slit-width  0.20  mm.  and  the  time  of  exposure  3  minutes.  No  exposure  was 
made  to  the  spark  in  this  instance.  The  temperatures  were  2°,  14°,  30°, 
45°,  60°,  70°,  and  81°  C. 

At  the  lowest  temperature  there  is  an  absorption  band  extending  from 
^  4800  to  A  5100.  As  the  temperature  rises  this  band  broadens,  the  broad- 


COBALT   SALTS.  35 

ening  being  quite  slow  at  first.  At  60°  the  limits  of  the  band  are  X  4700  to 
X  5600.  At  the  higher  temperatures  the  increase  in  the  absorption  through- 
out the  red  becomes  very  great,  and  at  81°  the  absorption  is  practically 
complete.  It  is  for  this  reason  that  the  cobalt  chloride  solution  becomes 
blue.  Bands  appear  at  X  6310  and  X  6440  at  72°  and  81°. 

Plate  13,  B,  gives  the  absorption  spectra  of  a  0.315  normal  concentra- 
tion and  a  depth  of  layer  of  10  mm.  This  solution  does  not  change  in  color 
and  shows  only  an  increased  widening  of  the  bands.  The  intense  absorp- 
tion in  the  red  does  not  take  place  under  these  conditions  of  concentration 
and  temperature. 

A  spectrogram  showing  the  effect  of  rise  in  temperature  was  made  for 
an  aqueous  solution  of  cobalt  chloride,  using  a  2.37  normal  solution,  and  a 
depth  of  cell  of  3  mm.  The  length  of  exposure  to  the  Nernst  glower  was 
2  minutes,  using  0.8  ampere  current  and  a  slit-width  of  0.20  mm.  The  length 
of  time  of  exposure  to  the  spark  was  5  minutes.  Starting  from  the  num- 
bered scale  the  temperatures  were  0°,  14°,  28°,  44°,  58°,  and  73°. 

The  region  of  the  spectrum  beyond  X  3000  is  absorbed.  The  amount 
of  this  absorption  does  not  vary  for  the  above  changes  in  temperature. 
Throughout  the  ultra-violet  region  of  the  spectrum  there  is  a  very  consider- 
able amount  of  general  absorption  of  light.  At  0°  there  is  a  wide  absorp- 
tion band  between  X  4500  and  X  5900.  The  ultra-violet  edge  of  this  band 
is  not  affected  by  change  in  temperature ;  the  edge  in  the  yellow,  however, 
widens  out  towards  the  longer  wave-lengths  with  rise  in  temperature. 
The  boundaries  of  this  edge  are  X  5900  at  0°,  X  5950  at  14°,  X  6000  at  28°, 
X  6050  at  44°,  and  X  6100  at  58°.  Above  60°  there  is  very  little  transmission 
in  the  red  end  of  the  spectrum. 

At  the  higher  temperatures  as  the  transmission  in  the  red  is  greatly 
decreased,  several  cobalt  bands  appear.  The  bands  at  XX  6300  and  6450 
are  of  about  equal  intensity  and  about  40  Angstrom  units  wide.  A  very 
faint  band  appears  at  about  X  6620. 

The  Wratten  and  Wainwright  films  are  sensitive  to  approximately 
X  7200  on  short  exposures.  At  0°  cobalt  chloride  allows  light  to  pass  with 
as  long  wave-lengths  as  can  record  themselves  on  the  films.  At  the  higher 
temperatures,  however,  this  is  not  the  case.  At  44°  the  light  beyond  X  7000 
is  absorbed,  and  at  60°  all  light  beyond  X  6800. 

A  spectrogram  showing  the  effect  of  rise  in  temperature  was  made  for 
an  aqueous  solution  of  cobalt  chloride  of  2.37  normal  concentration  and 
1  mm.  depth  of  cell.  The  length  of  exposure  to  the  Nernst  glower  was  3 
minutes,  current  0.7  ampere,  slit-width  0.20  mm.  The  exposure  to  the 
spark  was  for  3  minutes.  Starting  with  the  solution  next  to  the  numbered 
scale,  the  temperatures  were  1°,  12°,  27°,  45°,  60°,  70°,  and  85°. 

The  spectrum  in  the  ultra-violet  beyond  X  3000  was  completely  ab- 
sorbed by  the  cobalt  chloride.  The  whole  region  between.  X  3000  and 
X  5000  is  a  region  of  considerable  absorption,  possibly  half  of  the  light  being 
transmitted.  Between  X  5000  and  X  5600  there  is  an  absorption  band  with 
diffuse  edges.  This  absorption  gradually  widens  with  rise  in  temperature 
until  at  85°  it  extends  from  X  5000  to  X  5800;  the  widening  being  slightly 
unsymmetrical. 


36  A    STUDY    OF   THE    ABSORPTION    SPECTRA. 

The  cobalt  bands  XX  6315  and  6440  appear  in  the  spectrum  strip  taken 
at  85°.  At  this  temperature  there  is  a  very  large  amount  of  general  absorp- 
tion from  X  5800  on  to  X  6800.  Beyond  X  6800  the  absorption  is  complete. 
The  faint  band  at  X  6620  also  appears  at  this  temperature.  The  bands 
XX  6315  and  6440  appear  at  lower  temperatures,  but  the  transmission  is  so 
great  for  the  long  exposures  necessary  for  the  other  regions  of  the  spectrum 
that  the  bands  are  almost  obliterated. 

A  spectrogram  (Plate  15,  .A)  showing  the  effect  of  rise  in  temperature 
was  made  for  an  aqueous  solution  of  cobalt  chloride  0.125  normal  concen- 
tration and  a  layer  12  mm.  long.  Exposures  of  4  minutes  were  made  to 
the  Nernst  glower,  current  0.8  ampere,  slit-width  0.20  mm.  The  time  of 
exposure  to  the  spark  was  6  minutes.  Starting  with  the  strip  next  to  the 
numbered  scale,  the  temperatures  were  5°,  18°,  38°,  52°,  64°,  and  83°. 

The  absorption  spectrum  of  cobalt  is  characterized  by  two  wide  bands 
in  the  visible  spectrum  and  an  ultra-violet  band.  At  5°  the  ultra-violet 
band  extends  to  X  2700.  As  the  temperature  rises  this  band  widens  slightly, 
its  edge  falling  at  about  X  2800  at  83°.  The  edge  of  this  absorption  band  is 
quite  sharp.  The  violet  band  extends  from  about  X  4000  to  X  4400  at  5°. 
This  band  is  very  diffuse,  there  being  considerable  transmission  throughout 
the  whole  extent  of  the  band.  The  yellow  band  extends  from  X  5500  to 
>l  6100  at  5°,  there  being  slight  general  transmission  also  throughout  the 
whole  extent  of  this  band.  Both  these  bands  gradually  broaden  with  rise 
in  temperature,  and  at  83°  the  limits  of  the  violet  band  are  XX  4000  and 
4600;  of  the  yellow  band  XX  5500  and  6400.  It  will  be  seen  that  these 
bands  widen  unsymmetrically,  the  short  wave-length  edges  remaining 
nearly  stationary,  while  the  long  wave-length  edges  recede  towards  the  red. 
The  amount  of  transmitted  light  in  the  red  region  from  >l  6400  to  >l  7000 
is  much  less  at  the  higher  temperatures. 

A  spectrogram  (Plate  13,  B)  was  made  of  an  aqueous  solution  of  cobalt 
chloride  of  0.315  normal  concentration  and  10.4  mm.  depth  of  cell.  The 
exposures  were  3  minutes  to  the  Nernst  glower;  the  current  being  0.7 
ampere  and  the  slit-width  0.20  mm.  Starting  with  the  strip  adjacent  to  the 
comparison  scale,  the  temperatures  were  2°,  14°,  30°,  44°,  60°,  75°,  and  81°. 

The  most  noticeable  effect  of  rise  in  temperature  on  the  absorption 
spectra  of  cobalt  chloride  is  to  widen  the  band  in  the  green.  At  1°  this 
band  extended  from  X  4900  to  X  5300,  at  45°  from  X  4800  to  X  5400.  Above 
this  temperature  the  band  widens  quite  rapidly,  and  at  83°  it  extends 
from  X  4500  to  X  5700.  The  widening  is  approximately  symmetrical. 

A  spectrogram  similar  to  the  one  described  above  was  made  with  a 
cobalt  chloride  solution  of  0.315  normal  concentration  and  a  depth  of  layer 
of  24  mm.  No  exposure  was  made  to  the  spark  at  all.  At  the  lowest  tem- 
perature, 4°,  the  whole  of  the  short  wave-length  spectrum  was  absorbed 
up  to  X  5700.  No  trace  of  the  cobalt  bands  in  the  red  was  noticeable. 

A  spectrogram  was  made  to  compare  with  the  one  described  immedi- 
ately above.  These  two  spectrograms  were  taken  under  the  same  condi- 
tions, and  with  the  same  amount  of  cobalt  chloride  in  the  path  of  the 
beam  of  light.  In  the  solution  used  for  the  spectrogram  now  being 
described,  the  concentration  was  2.52  normal  and  the  length  of  cell  3  mm. 


COBALT    SALTS.  37 

At  the  lower  temperatures  the  effect  of  rise  in  temperature  was  the 
same  for  both  solutions.  In  the  case  of  the  concentrated  solution  all  light 
was  practically  absorbed  at  70°,  a  narrow  transmission  band  in  the  blue 
being  the  only  light  not  absorbed.  At  about  50°  the  bands  in  the  red  appear. 
Their  wave-lengths  are  approximately  U  6100  and  6250. 

A  spectrogram  was  made  of  a  2.52  normal  concentration  of  cobalt 
chloride  in  water  and  having  a  depth  of  cell  of  1.3  mm.  This  spectrogram 
showed  an  extremely  diffuse  band  between  about  >14600  and  /I  5500.  Rise 
in  temperature  had  very  little  effect  on  absorption,  except  in  the  red  region, 
where  the  general  absorption  was  greatly  increased.  At  38°  the  cobalt 
bands  appear  and  increase  in  intensity  with  rise  in  temperature.  Their 
positions  are  about  U  6100  and  6250— the  same  positions  as  on  the  pre- 
vious plate. 

A  spectrogram  (Plate  14,  A)  was  made  showing  the  effect  of  rise  in 
temperature  on  a  0.0394  normal  concentration  of  cobalt  chloride  in  water. 
At  5°  the  cobalt  band  extended  from  ^  4400  to  A  5600.  At  75°  it  had  wid- 
ened out  to  >l  4300  and  /I  5750.  .For  a  dilute  solution  it  will  be  seen  that 
rise  in  temperature  produces  only  a  small  change  in  the  absorption  spectra. 

COBALT  NITRATE. 

A  spectrogram  (Plate  14,  B)  was  made  showing  the  absorption  spectra 
of  a  2.3  normal  aqueous  solution  of  cobalt  chloride  of  2  mm.  depth.  The 
exposures  to  the  Nernst  glower  were  for  3  minutes,  current  0.7  ampere  and 
slit-width  0.20  mm.  Starting  with  the  strip  adjacent  to  the  numbered 
scale,  the  temperatures  were  2°,  14°,  30°,  45°,  60°,  75°,  and  85°. 

The  effect  of  rise  in  temperature  on  the  absorption  spectrum  of 
cobalt  nitrate  was  not  great.  The  wide  band  in  the  yellow  extended  from 
i  4600  to  ^  5500  at  2°.  The  band  gradually  widened  with  rise  in  tempera- 
ture, and  at  85°  extended  from  ^  4450  to  approximately  X  5650. 

It  will  be  noticed  that  the  effect  of  rise  in  temperature  on  the  absorption 
spectra  of  cobalt  nitrate  is  very  small  compared  with  that  of  cobalt  chloride. 
Hartley  considered  that  salts  crystallizing  with  the  largest  amounts  of 
water  usually  showed  the  greatest  change  in  their  absorption  spectra  when 
heated.  These  two  cobalt  salts,  however,  both  crystallize  from  aqueous 
solutions  with  6  molecules  of  water. 

A  spectrogram  (Plate  15,  B)  was  made  of  cobalt  nitrate  in  water,  of 
0.287  normal  concentration  and  a  3  mm.  length  of  cell.  The  length  of 
exposure  to  the  Nernst  glower  was  2  minutes  and  to  the  spark  3  minutes. 
The  current  in  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm.  The 
temperatures,  starting  with  the  strip  nearest  the  comparison  spectrum 
were  13°,  27°,  42°,  61°,  73°,  and  85°. 

At  ordinary  temperatures  cobalt  nitrate  crystallizes  out  with  6  mole- 
cules of  water.  The  effect  of  rise  in  temperature  on  the  absorption  spectra 
of  cobalt  nitrate  at  this  concentration  was  very  small.  The  NO,  ultra- 
violet band  extended  to  about  >l  3300.  It  did  not  appear  to  be  affected 
in  the  least  by  the  change  in  temperature.  A  weak  band  from  ^  5000  to 
X  5200  appears  at  the  higher  temperatures,  increasing  in  intensity  slightly 
with  rise  in  temperature. 


38  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

COBALT  SULPHATE. 

A  spectrogram  (Plate  16,  A)  of  the  absorption  spectra  of  a  normal 
aqueous  solution  of  cobalt  sulphate  was  made  for  the  different  temperatures, 
6°,  19°,  36°,  49°,  64°,  and  80°;  the  strip  representing  the  lowest  temperature 
being  nearest  the  comparison  spectrum.  The  depth  of  cell  was  3  mm.,  the 
length  of  exposure  to  the  Nernst  glower  2  minutes,  to  the  spark  6  minutes. 
The  current  through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm. 

The  absorption  spectrum  of  cobalt  sulphate  under  these  conditions 
consists  at  6°  of  a  band  in  the  yellow  from  A  4900  to  >t  5250.  At  80°  this 
band  has  widened  almost  symmetrically  and  extends  from  X  4800  to  X  5400. 
Except  the  change  in  this  band  rise  in  temperature  produced  no  appre- 
ciable effect. 

COBALT  ACETATE. 

Two  spectrograms  were  made  of  cobalt  acetate  in  water;  the  first 
(Plate  17,  A)  being  of  normal  concentration  and  3  mm.  depth  of  cell,  and 
the  second  being  0.125  normal  concentration  and  24  mm.  depth  of  cell. 
Starting  with  the  strip  nearest  the  comparison  spectrum,  the  temperatures 
were  4°,  18°,  32°,  49°,  64°,  and  79°  for  the  concentrated  solution,  and  7°,  27°, 
47°,  61°,  73°,  and  81°  for  the  more  dilute  solution.  The  time  of  exposure 
for  each  concentration  was  6  minutes  to  the  spark  and  2  minutes  to  the 
Nernst  glower,  current  being  0.8  ampere  and  slit-width  0.20  mm. 

At  the  lowest  temperature  there  was  transmission  in  the  ultra-violet 
out  to  >l  2400.  This  transmission  decreased  with  rise  in  temperature,  and 
at  80°  extended  to  A  2600  for  both  concentrations.  For  the  yellow-green 
band,  however,  the  effect  of  temperature  was  much  greater  in  the  case  of 
the  concentrated  solution.  For  the  more  concentrated  solution  at  4°  the 
yellow-green  band  extended  from  A  4900  to  A  5400.  As  the  temperature 
was  raised  it  increased  in  width  until  at  64°  it  extended  from  A  4600  to  A  5700. 
The  widening  produced  by  heating  the  solution  to  79°  from  64°  is  unsym- 
metrical,  the  band  now  extending  from  X  4550  to  A  6000.  For  the  dilute 
solution  at  70°  the  yellow-green  band  extends  from  A  4900  to  A  5300,  and 
at  81°  from  approximately  >l  4650  to  A  5600.  This  yellow-green  band  has 
very  diffuse  edges  and  there  is  usually  a  slight  general  transmission  through- 
out the  whole  extent  of  the  band. 

COBALT  CHLORIDE  AND  CALCIUM  CHLORIDE. 

A  spectrogram  (Plate  18,  A)  was  made  to  show  the  effect  of  rise  in 
temperature  on  a  mixture  of  cobalt  chloride  and  calcium  chloride  in  water. 
The  concentration  of  the  cobalt  chloride  was  0.237  normal  and  of  the  cal- 
cium chloride  4.14  normal.  The  length  of  layer  was  2  mm.  The  exposure 
to  the  Nernst  glower  was  for  3  minutes;  the  current  being  0.7  ampere  and 
the  slit-width  0.20  mm.  The  length  of  exposure  to  the  spark  was  3  min- 
utes. Starting  with  the  strip  nearest  the  comparison  scale,  the  temperatures 
were  2°,  15°,  30°,  42°,  60°,  75°,  and  85°. 

Throughout  the  whole  ultra-violet  region  there  was  strong  absorption, 
but  this  did  not  indicate  the  existence  of  any  banded  structure.  The  only 
portion  of  the  spectrum  showing  any  change  due  to  temperature  was  at 
the  red  end  of  the  spectrum.  The  increase  of  absorption  in  this  region  will 


COBALT  SALTS.  39 

be  given  for  each  temperature.  At  2°  there  was  transmission  to  A  7100, 
below  which  the  film  was  but  slightly  sensitive;  at  15°  the  limit  of  trans- 
mission being  A  6900;  at  30°  A  6700,  while  at  the  same  time  the  cobalt  bands 
appear;  at  42°  the  whole  region  from  A  6050  to  A  6500  is  very  weak  and  shows 
the  cobalt  bands  at  U  6105,  6240,  and  6415;  at  60°  the  limit  of  transmission 
is  at  >l  6000;  at  75°  A  5900,  and  at  85°  A  5800. 

COBALT  CHLORIDE  AND  ALUMINIUM  CHLORIDE. 

A  spectrogram  (Plate  18,  B)  was  made  showing  the  effect  of  rise  in 
temperature  on  the  absorption  spectra  of  an  aqueous  solution  of  0.161 
normal  cobalt  chloride  and  2.75  normal  aluminium  chloride.  The  depth 
of  layer  was  2  mm.  The  length  of  exposure  to  the  Nernst  glower  was  3 
minutes,  current  0.7  ampere,  and  slit-width  0.20  mm.  Starting  with  the 
strip  nearest  the  numbered  scale,  the  temperatures  were  —1.5°,  13°,  31°, 
45°,  60°,  72°,  and  87°. 

As  no  spark  was  used  there  is  of  course  no  impression  on  the  photo- 
graphic film  in  the  ultra-violet.  The  only  region  of  absorption  is  in  the 
red  and  this  increases  very  rapidly  with  rise  in  temperature.  The  cobalt 
bands  appear  at  —1°.  At  —1°  the  transmission  extends  to  X  6900;  at  13° 
to  A  6800;  at  31°  there  is  almost  complete  absorption  to  A  6100.  The  co- 
balt bands  do  appear  approximately  at  >U  6100,  6150  and  6420;  at  45°  the 
absorption  extends  to  A  6050;  at  60°  to  A  5950;  at  72°  to  X  6900,  and  at  87° 
to  /I  5850. 

A  spectrogram  (Plate  19,  A)  was  made  to  test  the  effect  of  rise  in 
temperature  on  the  change  in  the  absorption  spectra  of  a  dilute  solution  of 
cobalt  chloride  (0.00316  normal)  in  a  concentrated  (3.06  normal)  solution  of 
aluminium  chloride  in  water.  The  length  of  layer  was  150  mm.  The  time 
of  exposure  was  2  minutes  to  the  Nernst  glower  and  4  minutes  to  the  spark. 
The  current  through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm. 
Starting  with  the  strip  adjacent  to  the  comparison  scale,  the  temperatures 
were  1°,  18°,  41°,  55°,  68°,  and  85°. 

The  effect  of  rise  in  temperature  in  this  case  was  greater  than  in  that 
of  a  more  concentrated  solution  of  cobalt  chloride.  There  is  absorption  in 
the  whole  violet  region,  so  that  the  spectrum  at  1°  consists  simply  of  a 
transmission  from  A  4000  to  A  6500.  The  transmission  is  weak  from  A  6100 
to  X  6500  and  shows  the  cobalt  bands  at  AA  6100,  6350  (about  100  Angstrom 
units  wide),  and  6420.  At  18°  the  transmission  band  runs  from  A  4000  to 
A  6050.  With  rise  in  temperature  the  transmission  band  narrows  and  at  85° 
extends  only  from  A  4300  to  A  6750.  Weak  bands  about  100  Angstrom 
units  wide  appear  at  U  5050  and  5300.  These  are  considerably  broader  at 
the  lower  temperatures. 

A  spectrogram  (Plate  19,  B)  was  made  to  show  the  effect  of  rise  in 
temperature  on  the  absorption  spectra  of  a  0.0095  normal  cobalt  chloride 
and  4.6  normal  calcium  chloride  solution  in  water.  The  depth  of  the  layer 
was  50  mm.,  the  length  of  exposure  to  the  Nernst  glower  3  minutes,  the 
current  0.7  ampere  and  the  slit-width  0.20  mm.  The  length  of  exposure 
to  the  spark  was  5  minutes.  The  temperatures,  starting  with  the  strip 
adjacent  to  the  comparison  scale,  were  - 1.5°,  20°,  30°,  45°,  57°,  74°,  and  88°. 


40  A    STUDY   OP   THE   ABSORPTION    SPECTRA. 

The  ultra-violet  absorption  reached  to  about  A  3000,  with  a  great  deal 
of  general  absorption  throughout  the  violet.  This  general  absorption 
increased  slightly  with  rise  in  temperature.  At  — 1.5°  there  was  transmis- 
sion to  A  6900,  and  at  20°  to  A  6800.  At  20°  and  30°  the  cobalt  bands  show 
quite  strongly  at  AA  6100,  6240,  6400.  At  45°  the  absorption  reaches  to 
A  6050,  at  57°  to  A  5950,  at  74°  to  A  5850,  and  at  88°  to  A  5800. 

Wide  bands  appear  at  approximately  X  5000  and  A  5300.  These  bands 
are  very  weak,  considerably  weaker  than  for  a  solution  of  cobalt  chloride 
and  aluminium  chloride. 

COBALT  SULPHOCYANATE. 

A  spectrogram  (Plate  20,  A)  was  made  to  show  the  effect  of  change  in 
temperature  on  a  2-normal  aqueous  solution  of  cobalt  sulphocyanate 
(CoSzCjNj),  1  mm.  deep.  The  length  of  exposure  was  3  minutes  to  the 
Nernst  glower,  the  current  being  0.8  ampere  and  the  slit-width  0.20  mm. 
The  length  of  exposure  to  the  spark  was  6  minutes.  Starting  with  the  strip 
nearest  the  comparison  scale,  the  temperatures  were  3°,  18°,  31°,  45°,  59°, 
and  80°. 

Under  these  conditions  of  concentration  and  depth  of  layer  the  cobalt 
sulphocyanate  absorption  consists  of  an  ultra-violet  absorption  band  and 
a  wide  band  in  the  yellow  and  green.  As  the  temperature  is  raised  these 
bands  both  widen  out  on  the  red  side.  The  effect  of  temperature  is  espe- 
cially marked  between  60°  and  80°.  The  limits  of  the  ultra-violet  absorp- 
tion are  A  3400  at  3°,  A  3450  at  18°,  A  3450  at  31°,  A  3500  at  45°,  A  3550  at 
59°,  and  A  3600  at  80°. 

For  the  yellow-green  band  the  limits  are  A  4550  to  A  5600  at  3°,  A  4550 
to  A  5630  at  18°,  A  4550  to  X  5650  at  31°,  A  4570  to  A  5700  at  45°,  A  4550  to 
A  5750  at  59°,  and  A  4550  to  A  6400  at  80°.  At  59°  there  is  a  weak  and  broad 
band  extending  from  A  6000  to  about  A  6300. 

The  remarkable  feature  of  this  spectrogram  is  that  the  yellow-green 
band  widens  only  on  the  red  side. 

A  spectrogram  (Plate  20,  B)  was  made  of  a  much  more  dilute  solution 
of  cobalt  sulphocyanate  in  water,  the  concentration  being  0.25  normal 
and  the  depth  of  cell  8  mm.  The  time  of  exposure  to  the  Nernst  glower  with 
a  current  of  0.8  ampere  and  a  slit -width  of  0.20  mm.  was  2  minutes.  The 
length  of  exposure  to  the  spark  was  6  minutes.  Starting  with  the  strip 
adjacent  to  the  comparison  spectrum,  the  temperatures  were  6°,  20°,  33°, 
47°,  59°,  73°,  and  80°. 

In  this  spectrogram  the  effect  of  temperature  on  the  absorption 
spectra  of  cobalt  sulphocyanate  was  very  small  as  compared  with  the 
effect  on  the  2-normal  solution.  At  6°  the  ultra-violet  band  absorbed  pretty 
completely  up  to  A  3220.  There  was  a  slight  transmission  of  light  where  a 
strong  spark-line  was  located,  but  this  was  small.  The  edge  of  the  band 
was  quite  sharp.  The  yellow-green  band  extended  from  A  4600  to  A  5500. 
At  80°  the  ultra-violet  band  has  absorbed  everything  to  A  3300.  The  yellow- 
green  band  at  this  temperature  runs  from  A  4600  to  A  5600,  showing  a  slight 
widening  on  the  side  of  the  longer  wave-lengths. 


COBALT    SALTS. 


41 


COBALT  CHLORIDE  IN  WATER;  CONDUCTIVITY  AND  DISSOCIATION. 
The  conductivities  of  solutions  of  cobalt  chloride  at  the  temperatures 
35°,  50°,  and  65°  were  determined,  and  the  approximate  dissociations  at 
these  temperatures  calculated.  The  hydrolysis  especially  at  the  more 
elevated  temperatures  made  it  impossible  to  calculate  the  dissociations 
accurately,  v  is  the  volume,  pv  the  molecular  conductivity. 


Temperature  coefficients. 

35°. 

60°. 

65°. 

F. 

35°  to  50°. 

60°  to  65°. 

Cond. 
units. 

Per  cent. 

Cond 
units. 

Per  cent. 

4 

188.3 

66.1 

226.4 

61.4 

274.3 

59.2 

2.54 

1.35 

3.19 

1.41 

8 

197.6 

69.3 

249.4 

67.6 

302.5 

65.3 

3.45 

1.74 

3.54 

1.42 

32 

227.7 

79.9 

288.7 

78.3 

355.6 

76.8 

4.07 

1.79 

4.46 

1.54 

128 

255.1 

89.5 

326.7 

88.6 

404.2 

87.3 

4.77 

1.87 

5.17 

1.58 

512 

275.5 

96.6 

352.2 

95.5 

442.8 

95.6 

5.11 

1.86 

6.04 

1.71 

1024 

285.1 

100.0 

368.7 

100.0 

463.2 

100.0 

5.57 

1.95 

6.30 

1.71 

COBALT  BROMIDE  IN  WATER;  CONDUCTIVITY  AND  DISSOCIATION. 


Temperature  coefficienta. 

35°. 

50°. 

65°. 

Y 

35°  to  50°. 

50°  to  65°. 

pt> 

a 

HV 

a 

MV 

a 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

189.8 

65.7 

239.0 

64.5 

289.6 

62.4 

3.28 

1.73 

3.37 

1.41 

8 

205.1 

71.0 

259.4 

70.0 

315.7 

68.0 

3.60 

1.75 

3.75 

1.44 

32 

235.6 

81.5 

299.5 

80.8 

367.3 

79.1 

4.26 

1.81 

4.52 

1.51 

128 

258.0 

89.3 

329.5 

88.9 

406.7 

87.6 

4.77 

1.85 

5.15 

1.56 

512 

275.6 

95.4 

353.1 

95.3 

436.6 

94.0 

5.12 

1.87 

5.57 

1.58 

2048 

289.0 

100.0 

370.6 

100.0 

464.3 

100.0 

5.44 

1.88 

6.25 

1.68 

COBALT  NITRATE  IN  WATER;  CONDUCTIVITY  AND  DISSOCIATION. 
Cobalt  nitrate,  like  cobalt  chloride,  is  somewhat  hydrolyzed  in  dilute 
solutions.    The  dissociations  a  are,  therefore,  only  approximations. 


Temperature  coefficienta. 

36°. 

60°. 

65°. 

V. 

35°  to  60°. 

60°  to  66°. 

/*v 

a 

nv 

« 

M» 

a 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

172.8 

62.2 

216.8 

61.0 

263.5 

60.0 

2.93 

1.69 

3.11 

.43 

8 

190.7 

68.7 

239.7 

67.5 

291.4 

66.4 

3.27 

1.71 

3.45 

.44 

52 

218.5 

78.7 

276.9 

77.9 

340.2 

77.5 

3.89 

1.78 

4.22 

.52 

128 

244.0 

87.9 

310.1 

87.3 

384.0 

87.5 

4.41 

1.81 

4.93 

.59 

512 

262.9 

94.7 

334.7 

94.2 

414.6 

94.4 

4.79 

1.82 

5.33 

.59 

2048 

277.7 

100.0 

355.3 

100.0 

439.0 

100.0 

5.17 

1.86 

5.58 

.57 

42  A   STUDY  OF  THE   ABSORPTION   SPECTRA. 


SUMMARY. 

Glycerol  solutions  of  the  cobalt  salts  investigated  were  found  not  to 
show  any  of  the  fine  red  cobalt  bands.  Rise  in  temperature  of  the  more 
concentrated  solutions  caused  the  yellow  absorption  band  at  ^5100  to 
widen  and  to  broaden  out,  so  as  finally  to  absorb  all  the  red  and  thus  cause 
the  solution  to  appear  blue. 

Concentrated  aqueous  solutions  of  cobalt  chloride  show  an  enormous 
increase  in  the  absorption  with  rise  in  temperature.  Between  quite  narrow 
ranges  of  temperature  there  is  a  very  great  increase  in  the  red  absorption 
in  the  region  of  the  finer  bands.  As  the  concentration  is  increased  the 
temperature  at  which  this  great  increase  in  the  absorption  takes  place  is 
lowered.  For  the  more  dilute  solutions  the  widening  of  the  absorption 
with  rise  in  temperature  is  quite  symmetrical. 

The  effect  of  rise  in  temperature  on  the  absorption  of  cobalt  nitrate 
and  cobalt  sulphate  is  quite  small  as  compared  with  the  effect  on  the 
chloride. 

The  presence  of  calcium  or  aluminium  chloride  with  cobalt  chloride 
in  water  causes  the  effect  of  temperature  on  the  absorption  to  be  greater, 
and  causes  the  red  absorption  to  take  place  in  more  dilute  solutions,  than 
it  does  in  pure  cobalt  chloride  solutions.  The  temperature  at  which  the 
absorption  in  the  red  increases  so  greatly  may  be  called  the  "  critical  color 
temperature." 

The  "  critical  color  temperature  "  seems  to  depend  upon  the  existence 
of  some  solvate  or  peculiar  condition  of  the  cobalt  molecule.  The  critical 
color  temperature  is  much  higher  in  water  and  glycerol  than  for  other 
solvents.  In  a  similar  manner  the  water  and  glycerol  bands  are  more 
persistent  than  the  alcohol  or  acetone  bands.  It  is  important  that  a  com- 
plete study  be  made  of  the  critical  color  temperature  for  the  various  cobalt 
salts,  and  for  the  same  salt  in  different  solvents  and  when  mixed  with  other 
salts.  At  the  same  time  a  study  of  the  characteristic  cobalt  bands  could 
be  made. 

A  preliminary  test  was  made  to  find  if  the  presence  of  NOS  and  water 
had  the  same  hypsochromous  effect  *  on  the  cobalt  bands  as  it  has  on  the 
uranyl  bands.  Unfortunately  no  bands  of  any  strength  have  as  yet  been 
detected  for  cobalt  nitrate  in  water. 

1  Strong:  Phys.  Rev.,  29,  555  (1909). 


CHAPTER  V. 
NICKEL  SALTS. 

Introduction.— Nickel  chloride.— Nickel  sulphate.— Nickel  acetate.— Conductivity  data. 

INTRODUCTION. 

Among  the  more  recent  investigations  on  nickel  salts  may  be  mentioned 
those  of  Muller  *  and  Jones  and  Anderson  2.  Miiller  found  that  Beer's  law 
holds  for  solutions  of  nickel  nitrate  and  sulphate,  but  that  the  chloride  and 
bromide  showed  variations  from  the  law.  He  concludes  that  both  hydra- 
tion  and  aggregation  play  a  part  in  producing  these  variations  from  Beer's 
law. 

Jones  and  Anderson 2  find  that  Beer's  law  holds  for  the  chloride, 
sulphate  and  approximately  for  the  acetate.  Rather  narrow  bands  were 
found  at  M  6110,  6250,  and  6440  for  a  mixture  of  nickel  and  aluminium 
chlorides.  This  is  another  example  of  the  effect  of  the  presence  of  alumin- 
ium or  calcium  chloride.  Further  work  should  be  done  on  the  effect  of 
the  presence  of  these  salts  and  of  free  hydrochloric  acid.  The  investiga- 
tions should  be  carried  out  at  low  temperatures. 

NICKEL  CHLORIDE. 

A  spectrogram  showing  the  effect  of  rise  in  temperature  was  made  for 
an  aqueous  solution  of  nickel  chloride,  2.66  normal  concentration  and  3  mm. 
length  of  layer.  The  length  of  exposure  to  the  Nernst  glower  was  2  minutes, 
current  0.8  ampere  and  slit-width  0.20  mm.  The  exposure  to  the  spark 
was  for  5  minutes.  Starting  with  the  strip  next  the  numbered  scale,  the 
temperatures  are  -2°,  14°,  29°,  44°,  58°,  70°,  and  84°  C. 

The  absorption  of  nickel  chloride  consists  of  a  band  which  absorbs 
the  ultra-violet,  violet,  and  blue  portions  of  the  spectrum.  At  the  low 
temperatures  there  is  a  small  transmission  in  the  blue,  but  at  —  2°  practically 
all  light  is  absorbed  up  to  X  4200.  As  the  temperature  is  raised  the  absorp- 
tion extends  towards  the  region  of  greater  wave-lengths;  at  44°  it  is  at  X  4400 
and  at  84°  at  X  4600.  The  transmission  extends  into  the  red  as  far  as  the 
films  are  sensitive. 

A  spectrogram  (Plate  21,  B)  was  made  of  an  aqueous  solution  of  a  2.66 
normal  concentration  of  nickel  chloride  of  2  mm.  depth  of  layer.  The 
length  of  exposure  to  the  Nernst  glower  was  2  minutes  and  to  the  spark 
6  minutes.  The  current  through  the  Nernst  glower  was  0.8  ampere  and 
the  slit- width  0.20  mm.  Starting  with  the  strip  adjacent  to  the  numbered 
scale,  the  temperatures  of  exposure  were  5°,  18°,  30°,  44°,  57°,  75°,  and  85°. 

At  the  lower  temperatures  there  is  complete  absorption  of  almost  all 
the  shorter  wave-lengths  up  to  X  4250  at  5°.  There  is  an  exception  not 
shown  in  the  printed  spectrogram,  and  this  is  a  very  faint  transmission 

»  Ann.  Phys.,  12,  767  (1903)  ;  21,  515  (1906). 

'The  Absorption  Spectra  of  Solutions,  Carnegie  Institution  of  Washington  Pub.  No.  110. 

43 


44  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

about  X  2800.  With  rise  in  temperature  this  transmission  band  gradually 
weakens  and  at  60°  has  practically  disappeared. 

The  long  wave-length  edge  of  the  absorption  band  widens  uniformly 
with  rise  in  temperature  from  >l  4250  at  5°  to  A  4500  at  85°. 

A  spectrogram  (Plate  21,  A)  was  made  of  a  0.332  normal  aqueous 
solution  of  nickel  chloride  of  16  mm.  depth  of  layer.  The  length  of  expos- 
ure was  2  minutes  to  the  Nernst  glower,  and  6  minutes  to  the  spark.  The 
current  through  the  Nernst  glower  was  0.8  ampere  and  the  slit-width  0.20 
mm.  Starting  with  the  strip  nearest  the  comparison  spectrum,  the  tem- 
peratures of  exposure  were  5°,  19°,  33°,  45°,  60°,  71°,  and  82°. 

The  absorption  spectrum  of  nickel  chloride  under  the  above  conditions 
consists  of  a  band  in  the  violet,  and  more  or  less  complete  absorption  in  the 
extreme  ultra-violet.  At  5°  there  is  practically  complete  absorption  to 
/I  2600.  A  diffuse  absorption  band  runs  from  about  X  3700  to  X  4000.  As 
the  temperature  is  raised  the  transmission  in  the  ultra-violet  is  somewhat 
increased.  This  is  very  peculiar,  and  is  the  first  case  thus  far  noticed  of 
transmission  increasing  in  the  ultra-violet  with  rise  in  temperature.  At 
71°  the  violet  band  has  widened  out  so  as  to  extend  from  A  3700  to  X  4250. 

NICKEL  SULPHATE. 

A  spectrogram  (Plate  16,  B)  was  made  of  the  absorption  spectra  of  a 
2-normal  aqueous  solution  of  nickel  sulphate  3  mm.  deep.  The  length  of 
exposure  to  the  Nernst  glower  was  2  minutes  and  to  the  spark  6  minutes. 
The  current  through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm. 
Starting  with  the  strip  nearest  the  comparison  spectrum  the  temperatures 
were  5°,  19°,  32°,  47°,  61°,  72°,  and  81°. 

Nickel  sulphate  is  remarkable  for  the  fact  that  it  has  practically  no 
absorption  in  the  ultra-violet.  The  violet  band  at  5°  extends  from  X  3700 
to  X  4200,  and  at  81°  from  X  3700  to  X  4350.  It  will  thus  be  seen  that  the 
effect  of  temperature  on  the  absorption  spectrum  of  nickel  sulphate  is 
very  small  and  consists  simply  in  the  violet  band  widening  slightly  in  the 
direction  of  the  red. 

NICKEL  ACETATE. 

A  spectrogram  (Plate  22,  A)  was  made  of  a  0.5  normal  aqueous  solution 
of  nickel  acetate,  the  depth  of  layer  being  9  mm.  The  length  of  exposure 
to  the  Nernst  glower  was  2  minutes,  and  to  the  spark  6  minutes.  The 
current  in  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm.  Starting 
with  the  strip  nearest  the  comparison  spectrum,  the  temperatures  were  6°, 
23°,  38°,  52°,  64°,  74°,  and  84°. 

The  absorption  spectrum  of  nickel  acetate  is  characterized  by  a  band 
in  the  violet  and  a  slight  absorption  in  the  ultra-violet.  At  6°  the  absorp- 
tion in  the  ultra-violet  is  very  small.  At  84°  it  extends  to  about  A  2600. 
At  6°  the  violet  band  runs  from  A  3800  to  X  4150.  There  is  considerable 
transmission  in  this  region  at  the  lower  temperatures.  At  the  higher 
temperatures  the  limits  of  this  band  are  JU  3700  and  4400. 

A  spectrogram  (Plate  22,  B)  of  a  0.5  normal  solution  of  nickel  acetate 
in  water  was  made  for  various  temperatures  between  5°  and  81°,  the  depth 
of  layer  being  3  mm. 


NICKEL    SALTS. 


45 


At  5°  there  is  almost  complete  transmission  from  X  2300  to  A  7100. 
The  only  effect  of  rise  in  temperature  was  to  increase  slightly  the  absorption 
at  the  ultra-violet  end  of  the  spectrum  and  to  weaken  slightly  the  trans- 
mission in  the  region  A  4000. 

NICKEL  CHLORIDE  IN  WATER;  CONDUCTIVITY  AND  DISSOCIATION. 
Salts  of  nickel  like  those  of  cobalt  are  somewhat  hydrolyzed  at  the 
higher  temperatures  and  the  higher  dilutions. 


Temperature  coefficients. 

35°. 

80°. 

66°. 

35°  to  50°. 

50°  to  65°. 

MW 

- 

MB 

a 

M» 

a 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

174.9       61.1 

218.0 

59.3 

266.0 

58.4 

2.87 

1.64 

3.20 

1.46 

8 

194.5 

67.9 

247.3 

67.2 

301.5 

66.2 

3.52 

1.81 

3.61 

1.46 

32 

225.5 

78.8 

288.1 

78.3 

354.7 

77.9 

4.17 

1.85 

4.44 

1.54 

128 

251.4 

87.8 

321.4 

87.4 

398.4 

87.5 

4.66 

1.85 

5.13 

1.59 

512 

270.6  1    94.5 

344.4 

93.6 

426.1 

93.5 

4.92 

1.82 

5.45 

1.58 

2048 

286.2 

100.0 

367.9 

100.0 

455.5 

100.0 

5.45 

1.90 

5.84 

1.59 

NICKEL  NITRATE  IN  WATER;  CONDUCTIVITY  AND  DISSOCIATION. 


V. 

35°. 

60°. 

65°. 

Temperature  coefficients. 

36°  to  50°. 

50°  to  65°. 

P9 

a 

v-v 

a 

M» 

a 

Cond. 
units. 

Percent. 

Cond. 
units. 

Percent. 

4 
8 
32 

128 
512 
2048 

200.8 
216.8 
260.1 
289.7 
314.2 
329.3 

61.0 
65.8 
79.0 
89.8 
95.4 
100.0 

252.4 
276.3 
330.3 
369.2 
399.7 
(420.0)? 

60.1 
65.6 

78.6 
87.9 
95.2 
100.0 

306.6 
343.5 
402.4 
453.2 
494.8 
516.0 

59.4 
66.6 
78.0 
87.8 
95.9 
100.0 

3.44 
3.97 
4.68 
5.30 
5.70 
6.05 

1.71 

1.83 
1.80 
1.83 
1.81 

1.84 

3.61 
4.48 
4.81 
5.60 
6.34 
6.40 

1.43 
1.62 
1.46 
1.52 
1.59 
1.52 

CHAPTER  VI. 
COPPER   SALTS. 

Copper  bromide. — Copper  nitrate. 

A  fairly  concentrated  solution  of  copper  chloride  or  bromide  is  greenish 
brown,  while  dilute  solutions  are  blue.  The  addition  of  aluminium  or  cal- 
cium chloride  to  a  blue  dilute  solution  of  copper  chloride  changes  the  color 
to  green.  Uhler  has  investigated  the  effect  of  "  dehydrating  "  agents,  and 
also  dissolved  the  copper  salts  in  different  solvents.  Jones  and  Anderson 
have  extended  the  investigations  of  Uhler.  They  consider  that  the  ultra- 
violet band  must  be  due  to  the  copper  molecule  rather  than  to  the  ion. 
They  consider  from  the  way  this  band  is  affected  by  concentration  that  the 
absorbing  power  of  the  molecule  is  greatly  affected  by  its  immediate  sur- 
roundings. The  absorption  band  in  the  red,  like  the  green  cobalt  band, 
they  consider  to  be  due  to  the  metallic  atom. 

COPPER  BROMIDE. 

Two  spectrograms  were  made  of  the  absorption  spectra  of  copper 
bromide  in  water  as  affected  by  change  in  temperature.  The  first  spectro- 
gram (Plate  23,  4)  gives  the  absorption  of  a  2.06  normal  solution  of  copper 
bromide  1  mm.  thick  and  the  second  (Plate  23,  B)  a  0.25  normal  solution 
8  mm.  thick.  The  time  of  exposure  to  the  Nernst  glower  was  2  minutes, 
current  0.8  ampere  and  slit-width  0.20  mm.  The  time  of  exposure  to  the 
spark  was  6  minutes.  Starting  with  the  strip  nearest  the  comparison 
scale,  the  temperatures  were  6°,  17°,  30°,  and  45°  for  the  concentrated  solu- 
tion, and  6°,  17°,  31°,  46°,  59°,  71°,  and  85°  for  the  dilute  solution. 

The  effect  of  change  in  temperature  on  the  absorption  of  light  by 
this  salt  is  very  great,  especially  for  the  concentrated  solutions.  Above  45° 
not  enough  light  was  transmitted  to  affect  the  photographic  plate  in  any 
part  of  the  spectrum.  At  6°  a  very  faint  transmission  region  runs  from 
X  5600  to  A  6600  for  the  2.06  normal  solution.  At  45°  there  is  a  very  feeble 
transmission  about  200  Angstrom  units  wide  at  A  6400. 

The  dilute  solution  shows  apparently  complete  transmission  at  6°  be- 
tween M  3600  to  6800.  As  the  temperature  is  raised  this  transmission  band 
widens,  and  at  85°  it  extends  from  A  4100  to  A  6700. 

COPPER  NITRATE. 

Two  spectrograms  were  made  of  aqueous  solutions  of  copper  nitrate, 
the  one  (Plate  24,  A)  being  4.04  normal  and  having  a  depth  of  cell  of  2  mm.; 
and  the  second  one  (Plate  24,  B)  being  0.505  normal  and  a  depth  of  layer 
of  16  mm.;  the  amount  of  copper  nitrate  being  the  same  in  both  cases. 
For  the  first  spectrogram  the  time  of  exposure  to  the  Nernst  filament  was 
2  minutes  and  for  the  second  spectrogram  3  minutes,  the  current  being 
0.8  ampere  and  the  slit-width  0.20  mm.  Starting  with  the  strip  adjacent 
to  the  comparison  spectrum,  the  temperatures  were  5°,  15°,  30°,  45°,  60°, 

47 


48  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

76°,  and  87°  for  the  concentrated  solution,  and  1°,  15°,  30°,  45°,  60°,  75°, 
and  82°  for  the  dilute  solution.  At  5°  the  concentrated  solution  shows 
transmission  from  X  3600  to  X  6500,  at  87°  from  X  3800  to  A  6000.  For  the 
dilute  solution  there  is  practically  no  change  of  absorption  due  to  heating 
the  solution  from  1°  to  82°.  The  transmission  extends  from  A  3550  to 
J  6400. 

A  spectrogram  (Plate  25,  B)  was  made  of  a  copper  nitrate  solution  in 
water,  4.04  normal  concentration  and  3  mm.  length  of  layer  under  the 
same  conditions  as  for  the  other  copper  nitrate  solutions.  At  zero  tem- 
perature there  was  complete  transmission  from  X  3550  to  X  6000.  At  82° 
the  transmission  extended  from  A  3800  to  X  5900.  The  transmission  spec- 
trum was  cut  off  quite  sharply  and  completely  in  the  violet,  and  the  edge 
of  transmission  receded  towards  the  red  as  the  temperature  was  raised. 
The  long  wave-length  edge  of  the  transmission  band  was  but  slightly 
affected  by  change  in  temperature. 

Hartley  in  his  work  on  the  effect  of  temperature  on  absorption  spectra 
reaches  the  conclusion  that  the  salt  solutions  that  show  the  greatest  change 
in  their  absorption  spectra  as  the  temperature  is  changed,  are  those  that 
crystallize  with  the  greatest  amounts  of  water  of  crystallization.  The  cop- 
per salts  show,  however,  that  this  is  not  the  case;  since  of  all  these  salts 
the  bromide  shows  a  very  great  coefficient  of  temperature  change,  while 
the  nitrate  shows  a  much  smaller  change.  The  copper  salts  are  usually 
given  the  following  formulas  at  ordinary  room  temperatures:  CuCl2.2H20; 
CuBr2.2H2O;  CuSO4.5H2O;  Cu(NO3)2.3H2O.  In  many  cases,  however, 
Hartley's  rule  seems  to  hold  quite  well,  and  there  is  certainly  no  doubt 
that  the  water  of  combination  plays  a  very  important  role  in  the  absorp- 
tion of  light. 


CHAPTER  VII. 

CHROMIUM  SALTS. 

Introduction. — Chromium    chloride. — Chromium    nitrate. — Chromium  sulphate. 
Chromium  acetate. — Chrome  alum. — Conductivity  data. 

INTRODUCTION. 

A  fairly  large  number  of  investigators  have  worked  on  the  absorption 
spectra  of  compounds  of  chromium.  Some  of  these  have  studied  the  effect 
on  absorption  spectra  of  temperature,  concentration,  nature  of  the  solvent, 
etc.  In  the  following  introduction  to  this  chapter,  a  brief  discussion  of  the 
work  of  Hartley,  of  Jones  and  Anderson,  and  of  Bois  and  Elias  is  given. 

Hartley  found  for  the  green  chromium  chloride  that  at  20°  the  bands 
were  at  A  7040  to  X  6850,  and  A  6730  to  A  5380.  For  chromium  sulphate  he 
found  an  absorption  at  A  6000  at  100°,  and  at  A  5880  at  20°. 

Violet  chromium  sulphate  at  16°  gave  a  band  at  A  5430  (A  5620  to  A  5250) , 
and  at  100°  the  band  was  at  A  5510  (A  5770  to  A  5260). 

Chromium  nitrate,  a  violet-colored  salt,  at  16°  gave  an  absorption 
band  at  A  5920  (A  6270  to  A  5570),  and  at  50°  the  position  of  the  band  did  not 
change.  Practically  all  of  the  light  was  absorbed  at  100°. 

A  more  dilute  solution  of  chromium  nitrate  at  20°  gave  a  band  extend- 
ing from  A  5880  to  A  5570.  The  position  of  this  band  did  not  change  at  100°. 

Chromium  oxalate  was  found  to  give  a  band  extending  from  A  7060 
to  A  6850  at  20°,  and  blue  potassium  chromoxalate  (K6Gr2)  (C2O4)6.6H20,  a 
band  extending  from  A  6270  to  A  4970  at  20°,  and  from  A  6310  to  A  5030 
at  100°. 

Red  potassium  chromoxalate  K2Cr2(G2O4)4.10H2O  gave  narrow  bands 
at  A  6940  and  A  6850,  and  a  band  extending  from  A  6330  to  A  4780  at  20°, 
and  A  5880  to  A  3570  at  100°. 

Jones  and  Anderson  1  have  photographed  the  absorption  spectra  of 
chromium  chloride  and  nitrate  in  water.  For  chromium  chloride  they 
find  large  hazy  bands  at  A  4200  and  A  5900,  and  a  much  finer  band  at  A  6690. 
Chromium  nitrate  gives  very  similar  bands  at  A  4100,  A  5700,  and  A  6690. 
It  will  be  noticed  that  the  wide  nitrate  bands  have  shorter  wave-lengths 
than  the  corresponding  chloride  bands.  The  wave-lengths  given  by  them 
for  the  wide  cobalt  bands  bring  out  the  same  result.  The  cobalt  chloride 
bands  fall  at  A  3300  and  A  5200,  whereas  for  the  nitrate  the  latter  band  lies 
at  about  A  5100.  The  fact  seems  to  be  that  the  presence  of  the  NO3  group 
in  some  way  causes  the  absorption  bands  to  be  shoved  towards  the  violet. 
This  is  in  accord  with  a  paper  by  one  of  the  authors,2  where  it  was  shown 
that  the .  uranyl  nitrate  bands  have  shorter  wave-lengths  than  the  other 
uranyl  bands.  The  same  law  was  shown  to  hold  for  uranous  bands  and 
also  for  the  phosphorescent  bands  of  uranyl  salts.  The  presence  of  free 

1  Absorption  Spectra  of  Solutions,  Carnegie  Institution  of  Washington  Pub.  No.  110. 
1  Phys.  Rev.,  29,  6,  555,  Dec.  (1909). 

4  49 


50 


A    STUDY   OF   THE    ABSORPTION  SPECTRA. 


nitric  acid  causes  the  uranyl  nitrate  bands  to  shift  still  further  towards 
the  violet. 

Bois  and  Elias  l  have  investigated  the  effect  of  low  temperature  and 
a  magnetic  field  on  several  chromium  salts,  and  have  made  an  especially 
detailed  study  of  the  ruby. 

Chrome  alum  crystals  (KCr(SO<)2.12H2O)  at  18°  give  a  strong  band 
from  >l  6698  to  >l  6716.  At  - 190°  this  band  has  become  smaller,  ^  6684  to 
>l  6694,  and  is  shifted  about  17  Angstrom  units  to  the  violet.  A  strong  line 
appears  at  >l  6702  and  about  twenty  bands  occur  between  A  6190  and  A  7160. 
The  band  A  6686  to  >l  6694  was  slightly  affected  by  a  magnetic  field.  An 
aqueous  solution  shows  bands  at  U  6627,  6723  and  6875,  7275. 

Potassium  chromium  oxalate  (K6Cr2(C2O4)0.6H20)  at  18°  gives  a  band 
from  >l  6980  to  I  7032;  at  -  180°  X  6965  to  ^  7012,  a  shift  of  16  Angstrom 
units.  An  aqueous  solution  gives  bands  at  M  6953  to  6990  and  7084  to 
71 10.  At  18°  a  glycerol  solution  gives  a  band  at  U  6946  to  6990.  At  - 130° 
bands  appear  at  >U  6947,  6976;  6597,  6654;  6694,  6716;  6752,  6772. 

The  band  X  6925  of  potassium  chromium  oxalate  (K2Cr2(C2OJ4.zH20) 
is  slightly  broadened  by  a  magnetic  field.  Chromium  fluoride  mixed  with 
borax  gave  at  18°  two  bands  >U  6734,  6810,  and  6947,  7390;  at  -190° 
/U  6724,  6805  and  6923,  7476;  the  first  band  thus  shifting  about  8  Angstrom 
units  to  the  violet. 

The  most  important  chromium  compound  investigated  by  Bois  and 
Elias  was  the  ruby,  a  solid  solution  of  a  small  amount  of  Cr2O3  in  aluminium 
oxide,  A12O3.  Miethe  2  has  found  the  absorption  and  fluorescent  bands  to 
occupy  the  same  positions.  The  following  data  are  taken  from  the  paper 
of  Bois  and  Elias. 

Ordinary  absorption  spectra  of  the  ruby. 


At  18°. 

At  -190°. 

Shift. 

X  4470  weak  

A  4465  weak  

5  0 

A  4677  to  A  4691  weak  band  

A  4675  to  A  4684  strong  band  

4  5 

B,  A  4749  to  A  4757  strong  band  

A  4746  strong  line  

7  0 

B,  A  4765  to  A  4771  weak  band  

A  4763  weak  line  

5  0 

A  5140  to  A  5995     . 

!A  5028  to  A  5844 
A  5881  to  A  5912  strong  band. 

A  6575  to  A  6600  weak  band  

A  5960  to  A  5974  strong  band. 
I  A  6575  weak  line  

\  A  6586  weak  line  

A  6666  to  A  6701  weak  band  

A  6667  to  A  6689.   . 

R,  A  6924  to  A  6926  strong  band  

A  6918  strong  line  

7  o 

R,  A  6938  to  A  6941  very  strong  band. 

A  6932  very  strong  line 

7  5 

The  extraordinary  absorption  spectra  give  considerable  relative  dif- 
ferences in  the  relative  intensities  of  the  absorption  bands,  but  very  little 
if  any  difference  in  the  wave-lengths  of  the  finer  bands.  The  fluorescent 
bands  excited  either  by  arc  or  sunlight  occupied  the  same  positions  as  the 
absorption  bands.  A  detailed  account  is  given  of  the  effect  of  magnetic 
fields  of  different  strengths  upon  B2,  Bx,  R2,  and  Rt.  The  effect  of  a  mag- 


1  Ann.  Phys.,  27,  12,  247  (1908). 

"  Verb.  d.  deutsch.  physik.  Gesell.,  9,  715  (1907). 


CHROMIUM   SALTS.  51 

netic  field  on  R,  as  a  fluorescent  band  was  the  same  as  on  the  absorption 
band,  with  the  exception  of  the  polarization.  The  effect  of  the  magnetic 
field  also  seems  to  vary  slightly  with  the  temperature. 

CHROMIUM  CHLORIDE. 

An  aqueous  solution  of  chromium  chloride  of  0.53  normal  concentration 
and  2  mm.  depth  of  cell  shows  the  characteristic  chromium  bands.  The 
solution  in  question  had  its  absorption  spectrum  mapped  between  5°  and 
83°.  The  ultra-violet  band  extended  to  about  >l  2600,  its  edge  being  very 
broad.  It  was  but  slightly  affected  by  the  above  change  in  temperature. 
The  blue-violet  band  was  broadened  on  its  red  side  about  200  Angstrom 
units  by  the  above  rise  in  temperature.  The  yellow  band  at  5°  extended 
from  A  5500  to  ^  6100.  At  83°  it  extended  from  /I  5450  to  >l  6200.  There 
was  but  slight  widening  of  this  band  with  rise  in  temperature  on  the  short 
wave-length  side.  The  bands  in  the  red  do  not  appear. 

A  spectrogram  was  made  of  a  0.125  normal  aqueous  solution  of  chro- 
mium chloride  4  mm.  depth  of  layer.  Exposures  to  the  Nernst  glower  were 
3  minutes  in  length  and  to  the  spark  6  minutes.  The  current  through  the 
glower  was  0.7  ampere  and  the  slit-width  0.20  mm.  The  temperatures 
ranged  between  4°,  20°,  35°,  50°,  61°,  73°,  and  82°.  At  4°  the  blue-violet 
band  extended  from  A  4200  to  X  4400,  and  the  yellow  band  from  X  5200  to 
/I  6200.  At  82°  these  bands  had  widened  so  that  they  extended  from  >l  4150 
to  >l  4550  and  ^  5150  to  /I  6400,  respectively.  At  the  highest  temperature 
a  weak  band  appears  at  approximately  ^  6750.  The  band  is  very  weak 
and  diffuse. 

A  spectrogram  was  made  of  the  change  due  to  a  rise  in  temperature 
on  a  0.125  normal  chromium  chloride  solution  in  water  having  a  depth  of 
layer  of  4  mm.  The  solution  of  chromium  chloride  at  room  temperatures 
is  a  dull  green.  The  length  of  exposure  to  the  Nernst  glower  was  3  minutes, 
current  0.7  ampere  and  slit-width  0.20  mm.  The  length  of  exposure  to  the 
spark  was  6  minutes.  The  temperatures,  starting  with  the  lowest  strip, 
were  5°,  20°,  35°,  50°,  60°,  70°,  and  82°. 

At  5°  the  ultra-violet  absorption  was  complete  to  X  2600.  At  82°  this 
absorption  had  increased  so  as  to  extend  to  A  2700.  Over  the  remainder 
of  the  spectrum  there  was  transmission.  At  higher  temperatures  the 
transmission  was  much  weakened,  however,  at  ^  4300,  and  in  the  whole 
region  from  X  5000  to  A  6000. 

Another  spectrogram  was  made  in  exactly  the  same  manner  but  with 
a  deeper  length  of  layer.  At  5°  the  ultra-violet  band  for  this  solution 
reached  to  X  2700,  at  80°  to  ^  2800.  There  was  more  or  less  general  absorp- 
tion over  the  whole  region  of  the  spectrum,  and  this  general  absorption 
increased  quite  rapidly  with  rise  in  temperature,  especially  in  the  visible 
region.  At  the  higher  temperatures  there  was  almost  complete  absorption 
at  A  4300  and  from  >l  5700  to  X  6100.  These  very  diffuse  bands  broadened 
on  both  sides  with  rise  in  temperature,  the  broadening  of  the  yellow-green 
band  being,  however,  somewhat  greater  on  the  long  wave-length  edge. 
The  characteristic  bands  in  the  red  do  not  appear  even  at  the  higher  tem- 
peratures. 


52  A    STUDY    OF   THE    ABSORPTION  SPECTRA. 

CHROMIUM  CHLORIDE  AND  ALUMINIUM  CHLORIDE. 

A  spectrogram  (Plate  27,  A)  was  made  to  show  the  effect  of  rise  in 
temperature  on  a  mixture  of  chromium  chloride  and  aluminium  chloride 
in  water.  The  concentration  of  the  former  was  0.125  normal,  and  the 
latter  2.28  normal.  The  depth  of  cell  was  9  mm.  Exposures  of  4  minutes 
were  made  to  the  Nernst  glower  and  6  minutes  to  the  spark.  The  current 
through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm.  Starting 
with  the  strip  nearest  the  comparison  scale  the  temperatures  were  6°,  19°, 
36°,  51°,  66°,  and  81°. 

The  most  marked  effect  of  the  aluminium  chloride  was  the  production 
of  a  very  pronounced  unsymmetrical  broadening.  At  6°  the  ultra-violet 
band  reached  to  X  3000.  At  81°  it  had  widened  to  almost  X  3300,  a  greater 
widening  than  the  same  band  in  a  pure  chromium  chloride  aqueous  solution. 
At  6°  the  blue-violet  band  extends  from  A  4100  to  X  4600,  and  the  yellow 
band  from  A  5800  to  I  6200.  The  red  sides  of  the  blue-violet  and  yellow 
bands  not  only  widen  out  enormously  towards  the  red,  but  the  short  wave- 
length edges  of  these  bands  move  towards  the  red.  This  effect  is  a  continu- 
ous one,  but  is  much  greater  for  the  temperature  changes  from  51°  to  66° 
and  66°  to  81°.  At  81°  the  blue-violet  band  extends  from  X  4150  to  A  5050, 
and  the  yellow  band  from  A  5900  throughout  the  remainder  of  the  spectrum 
as  far  as  the  film  is  sensitive.  The  fine  bands  in  the  red  do  not  appear. 

CHROMIUM  CHLORIDE  AND  CALCIUM  CHLORIDE. 

A  spectrogram  (Plate  27,B)  was  made  of  a  mixture  of  chromium  chloride 
and  calcium  chloride  in  aqueous  solution,  the  chromium  chloride  being  of 
0.125  normal  concentration  and  the  calcium  chloride  of  3.45  normal  concen- 
tration. The  length  of  the  solution  was  9  mm.  The  exposures  to  the 
Nernst  glower  were  for  5  minutes  and  to  the  spark  6  minutes.  The  current 
through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm.  Starting 
with  the  strip  nearest  the  comparison  scale  the  temperatures  were  6°,  19°, 
31°,  45°,  64°,  and  80. 

The  effect  of  rise  in  temperature  on  this  solution  of  chromium  and 
calcium  chlorides  is  very  similar  to  that  on  chromium  and  aluminium 
chlorides.  In  this  case  the  widening  of  the  ultra-violet  band  is  greater 
and  practically  all  of  this  widening  takes  place  in  the  change  of  tempera- 
ture from  45°  to  64°  and  from  64°  to  80°.  In  this  case  the  blue-violet 
and  yellow  bands  widen  unsymmetrically,  and  here  too  the  short  wave- 
length edge  of  the  yellow  band  not  only  does  not  widen  but  actually  nar- 
rows with  rise  in  temperature.  The  blue-violet  band  widens  on  both 
edges,  the  greater  widening,  however,  being  on  the  red  side. 

At  6°  the  ultra-violet  band  extends  to  A  2800,  the  blue-violet  band 
from  A  4000  to  X  4400  and  the  yellow  band  from  A  5600  to  A  6100.  At  64° 
the  ultra-violet  band  extends  to  A  3100,  the  blue- violet  band  from  X  4000  to 
A  4600,  and  the  yellow  band  from  A  5650  to  A  6300.  At  80°  the  ultra-violet 
band  extends  to  A  3250,  the  blue-violet  band  from  A  3950  to  A  5000  and  the 
yellow  band  from  A  5700  throughout  the  red  end  of  the  spectrum  as  far  as 
the  film  is  sensitive. 


CHROMIUM   SALTS.  53 

CHROMIUM  NITRATE. 

Two  spectrograms  were  made  of  chromium  nitrate  in  water,  one 
(Plate  26,  A)  of  a  0.754  normal  concentration  and  3  mm.  depth  of  cell,  and 
the  other  (Plate  26,  E)  a  0.094  normal  concentration  and  24  mm.  depth  of 
cell.  The  concentrated  solution  was  exposed  2  minutes  and  the  dilute  solu- 
tion 3  minutes  to  the  Nernst  glower,  current  0.8  ampere  and  slit-width 
0.20  mm.  Both  spectrograms  were  made  using  a  6  minutes  exposure  to  the 
spark.  Starting  with  the  strip  nearest  the  comparison  scale  the  tempera- 
tures of  exposure  of  the  concentrated  solution  to  the  light  were  5°,  17°, 
32°,  45°,  60°,  70°,  and  81°,  and  of  the  dilute  solution  7°,  17°,  33°,  44°,  59°, 
69°,  and  83°. 

Chromium  nitrate  under  the  conditions  here  described  shows  three 
bands,  the  N03  band  in  the  ultra-violet,  a  band  in  the  blue  and  violet  and 
a  wide  band  in  the  yellow  and  green.  For  the  concentrated  solution  the 
temperature  effect  on  the  NO3  band  is  small,  the  absorption  being  about 
50  Angstrom  units  greater  at  the  higher  temperature.  At  5°  the  limit  of 
this  band  is  X  3220.  The  blue-violet  band  extends  from  X  3700  to  X  4500 
and  the  yellow-green  band  from  X  5100  to  X  6300  at  6°.  At  81°  the  blue- 
violet  band  extends  from  X  3700  to  X  4600  and  the  yellow-green  band  from 
X  5100  to  X  6450.  For  all  the  temperatures  there  was  a  band  at  about 
X  6750.  This  band  was  unaffected  by  temperature. 

At  7°  the  ultra-violet  band  of  the  more  dilute  solution  extends  to  X  3200 
and  is  about  50  Angstrom  units  wider  at  the  higher  temperature.  The  blue- 
violet  band  at  7°  runs  from  X  3650  to  X  4400,  at  83°  X  3750  to  X  4600.  The 
yellow-green  band  at  7°  runs  from  X  5400  to  X  6150.  At  83°  it  has  widened 
out  from  X  5350  to  X  6400. 

A  spectrogram  was  made  showing  the  effect  of  temperature  on  the 
absorption  spectra  of  a  0.754  normal  aqueous  solution  of  chromium  nitrate, 
the  depth  of  layer  being  1  mm.  The  times  of  exposure  were  5  minutes  to 
the  spark  and  2  minutes  to  the  Nernst  glower,  current  being  0.8  ampere  and 
width  of  slit  0.20  mm.  The  temperatures,  starting  with  the  strip  adja- 
cent to  the  comparison  spectrum,  were  5°,  17°,  30°,  44°,  58°,  72°,  and  82°. 

The  absorption  spectrum  of  chromium  nitrate  under  the  above  named 
conditions  consists  of  a  weak  transmission  band  at  X  2800.  At  5°  this  band 
is  about  300  Angstrom  units  wide.  As  the  temperature  is  raised  the 
transmission  weakens,  but  there  is  so  much  general  transmission  that  the 
stronger  spark  lines  usually  show  more  or  less  evenly  throughout  the  absorp- 
tion, which  at  5°  extends  from  X  3000  to  X  4200.  At  82°  there  is  a  complete 
absorption  of  all  the  short  wave-lengths  up  to  X  4500.  Like  all  other  bands 
for  chromium  solutions,  the  edges  are  very  broad  and  diffuse.  At  the  higher 
temperatures  there  seemed  to  be  somewhat  greater  absorption  in  the  red 
at  X  6800. 

CHROMIUM  SULPHATE. 

A  spectrogram  (Plate  28,  B)  was  made  of  an  aqueous  solution  of 
chromium  sulphate  of  0.125  normal  concentration  and  a  depth  of  cell  of 
3  mm.  The  length  of  exposure  was  4  minutes  to  the  Nernst  glower  at  0.8 
ampere,  and  6  minutes  to  the  spark.  The  slit-width  was  0.20  mm.  The 


54  A    STUDY   OF   THE    ABSORPTION  SPECTRA. 

temperatures,  starting  with  the  strip  nearest  the  numbered  scale,  were  5°, 
20°,  37°,  51°,  66°,  and  82°. 

At  5°  the  three  characteristic  chromium  bands  appear — the  ultra- 
violet band  extending  to  A  2800,  the  blue-violet  band  from  A  4100  to  A  4450 
and  the  yellow-green  band  from  X  5500  to  X  6200.  The  bands  at  X  6800 
appear  but  very  faintly.  Throughout  the  visible  portion  of  the  spectrum 
there  is  a  very  strong  absorption,  as  will  be  noticed  from  the  extremely 
long  exposure  of  4  minutes  to  the  Nernst  glower. 

At  82°  the  ultra-violet  band  extends  to  A  2900,  the  blue-violet  band 
from  A  4100  to  A  4550  and  the  yellow-green  band  from  A  5500  to  A  6300. 
The  effect  of  temperature  was  very  small,  being  in  general  the  shifting  of 
the  long  wave-length  edges  of  all  three  bands  towards  the  red. 

CHROMIUM  ACETATE. 

A  spectrogram  showing  the  effect  of  rise  in  temperature  on  the  absorp- 
tion spectra  of  a  10  mm.  solution  of  0.125  normal  chromium  acetate  was 
made.  The  slit-width  was  0.20  mm.  Exposures  were  made  to  the  Nernst 
glower  for  4  minutes,  the  current  being  0.8  ampere.  Exposures  to  the 
spark  were  continued  for  6  minutes.  Starting  with  the  strip  nearest 
the  comparison  scale,  the  temperatures  were  5°,  20°,  36°,  52°,  64°,  and  78°. 
The  absorption  remained  practically  independent  of  the  temperature. 

Chromium  acetate  under  the  present  conditions  of  concentration  and 
depth  of  cell  shows  a  faint  transmission  band  in  the  green  between  AA  5000 
and  5200.  Except  for  a  few  faint  bands  there  is  transmission  of  all  the 
longer  wave-lengths  beyond  A  6400.  The  whole  blue,  violet,  and  ultra- 
violet regions  are  absorbed,  as  is  also  the  whole  region  between  A  5200  and 
A  6400.  There  is  an  absorption  band  at  A  6490,  which  resembles  very  much 
one  of  the  larger  uranyl  bands.  It  is  about  60  Angstrdm  units  wide.  The 
short  wave-length  edge  of  this  band  is  very  diffuse  and  looks  very  much  as 
though  the  band  were  complex.  There  is  a  narrow  band  at  A  6550.  This 
band  is  but  10  Angstrom  units  wide.  Narrow  bands  very  much  like  this 
one  appear  at  AA  6510,  6800,  6860,  6920,  6970,  and  7030.  The  smaller 
bands  are  very  faint  and  in  the  spectrum-strip  at  78°  practically  disappear. 

A  spectrogram  was  made  of  chromium  acetate,  0.125  normal  concen- 
tration in  water  and  3  mm.  depth  of  cell.  The  exposures  were  3  minutes  to 
the  Nernst  glower  at  0.8  ampere,  and  slit-width  0.20  mm.  The  length  of 
exposure  to  the  spark  was  6  minutes.  The  temperatures  were  5°,  19°,  37°, 
50°,  64°,  and  79°. 

The  effect  of  change  in  temperature  in  this  chromium  salt  was  very 
email,  the  only  noticeable  change  being  a  slight  increase  in  the  intensity  of 
the  yellow  band.  The  whole  ultra-violet  was  absorbed  up  to  A  3800.  From 
A  3800  to  A  4600  there  was  a  very  strong  general  absorption.  There  was 
also  strong  absorption  in  the  yellow. 

CHROME  ALUM. 

A  spectrogram  (Plate  28,  A)  gives  the  effect  of  rise  in  temperature  on 
the  absorption  spectra  of  chrome  alum.  It  will  be  seen  that  the  violet  and 
ultra-violet  bands  are  widened  but  slightly.  The  other  chromium  band  in 
the  yellow  is  slightly  widened. 


CHROMIUM    SALTS. 


55 


CHROMIUM  CHLORIDE  IN  WATER — CONDUCTIVITY  AND  TEMPERATURE 
COEFFICIENTS. 

Chromium  chloride  is  considerably  hydrolyzed  at  the  higher  dilutions, 
and  at  the  higher  temperatures.  The  temperature  coefficients  are,  there- 
fore, not  quite  as  regular  as  with  the  other  salts,  and  even  approximate 
dissociations  can  not  be  calculated. 


Temperature  coefficients. 

35°. 

50°. 

66°. 

35°  to  60°. 

60°  to  65°. 

M« 

m> 

M 

Good, 
units. 

Per  cent. 

Cond. 
units. 

Percent. 

4 

201.3 

259.8 

329.9 

3.90 

1.94 

4.67 

.80 

8 

240.1    • 

313.4 

395.9 

4.88 

2.03 

5.50 

.75 

32 

301.1 

391.0 

489.0 

5.99 

1.99 

6.53 

.67 

128 

369.5 

483.3 

615.6 

7.59 

2.05 

8.82 

.82 

512 

438.6 

590.1 

761.6 

10.10 

2.30 

11.43 

.94 

2048 

523.5 

686.0 

871.1 

10.83 

2.06 

12.34 

.80 

CHROMIUM  NITRATE  IN  WATER — CONDUCTIVITY  AND  TEMPERATURE  COEFFICIENTS. 

Results  of  the  same  general  character  were  obtained  with  chromium 
nitrate  as  with  chromium  chloride.  On  account  of  the  hydrolysis  it  was 
impossible  to  calculate  the  dissociation. 


Temperature  coefficients. 

35°. 

60°. 

65°. 

y 

35°  to  60°. 

60°  to  65'. 

M 

M 

IMP 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

228.2 

289.7 

365.2 

4.10 

1.80 

5.03 

1.73 

8 

263.0 

334.7 

419.4 

4.78 

1.82 

5.65 

1.69 

32 

321.4 

414.8 

519.1 

6.23 

1.94 

6.95 

1.68 

128 

395.0 

517.6 

663.2 

8.17 

2.07 

9.71 

1.87 

512 

473.2 

627.6 

809.0 

10.23 

2.18 

12.09 

1.93 

2048 

554.3 

732.6 

937.4 

11.88 

2.14 

13.65 

1.86 

CHAPTER  VIII. 

ERBIUM  SALTS. 

Introduction. — Erbium  chloride  in  glycerol. — Erbium  chloride  in  water  as  affected  by  rise 
in  temperature. — Erbium  nitrate  and  other  salts. 

Of  all  compounds  known  those  of  erbium  probably  show  the  most 
characteristic  absorption  spectra  in  the  solid  state  and  in  solution.  The 
first  to  make  a  detailed  study  of  the  erbium  spectrum  was  H.  Becquerel.1 
One  of  the  minerals  that  he  studied  was  xenotine  or  hussakite,  a  uniaxial 
crystalline  compound  consisting  mainly  of  the  phosphates  of  yttrium  and 
erbium.  The  wave-lengths  of  the  ordinary  and  extraordinary  spectrum 
bands  are  given.  The  absorption  spectrum  observed  in  any  direction 
through  the  crystal  Becquerel  found  to  be  made  up  by  the  superposition  of 
two  series  of  bands,  one  corresponding  to  vibrations  normal  to  the  axis 
of  the  crystal  and  the  other  to  vibrations  parallel  to  this  axis. 

Schulz  2  has  worked  on  the  effect  of  a  magnetic  field  on  the  absorption 
spectrum  (obtained  by  reflection)  of  erbium  oxide.  He  finds  that  the  bands 
>U  4482.2,  4491.3,  4510.5,  4541.9,  4554.1,  4562.6,  4571.8,  4579.1,  4606.5, 
4625.9,  5197.0,  5205.5,  5242.2,  5261.0,  5387.7,  6430.0,  6476,  6496,  6524, 
6538,  6546,  6562,  6581,  6598,  6617,  and  6652  broaden  when  the  magnetic 
field  is  turned  on;  A  4482.2  is  shifted  to  the  red,  while  A  4510.5  and  A  4562.6 
are  shifted  towards  the  violet. 

Bois  and  Elias  3  have  made  a  very  thorough  study  of  the  absorption 
of  hussakite,  erbium  yttrium  sulphate,  erbium  nitrate  and  erbium  mag- 
nesium nitrate  at  18°  and  at  —190°  and  also  found  the  Zeeman  effect  at 
these  temperatures.  As  the  results  are  all  collected  in  the  above  reference 
no  detailed  account  will  here  be  given.  In  general,  the  bands  show  a  Zee- 
man effect.  Doublets  and  triplets  are  quite  common. 

A  very  extended  investigation  on  the  effect  of  low  temperatures  and 
magnetic  fields  on  the  absorption  spectra  of  erbium  has  been  made  by 
J.  Becquerel.  As  the  papers  of  Becquerel  are  somewhat  scattered,  a  rather 
full  account  of  them  will  be  given  here.  The  first  work  4  of  Becquerel  was 
upon  the  effect  of  a  magnetic  field  on  the  absorption  spectra  of  xenotine 
and  tysonite  at  ordinary  temperatures.  In  the  following  table  +  will 
signify  a  strong  band  and  +  +  a  very  strong  band.  Field  will  always  refer 
to  the  magnetic  field  which  in  this  work  is  usually  14,100  c.g.s.  units.  Units 
of  wave-length  are  stated  in  Angstrom  units. 

When  the  optic  axis  is  parallel  to  the  beam  of  light  a  crystal  behaves 
like  an  isotropic  body.  When  placed  in  a  magnetic  field,  however,  a  recti- 
linear vibration  is  transformed  into  an  elliptical  one.  This  is  Becquerel's 
magnetic  double-refraction.  The  effect  of  the  magnetic  field  on  vibrations 
normal  to  the  field  is  different  from  the  effect  on  vibrations  parallel  to 

1  Ann.  Chim.  Phys.  (6),  14,  194  (1888). 
1  Astrophys.  Journ.,  30,  383  (1909). 
8  Ann.  Phys.,  27,  279  (1908). 

«Compt.  rend.,  Mar.  26,  Apr.  21,  May  21,  Nov.  19,  Dec.  3,  Dec.  10,  Dec.  24  (1906): 
Jan.  21  (1907).     Le  Radium,  Feb.  (1907). 

57 


58 


A    STUDY   OF   THE   ABSORPTION    SPECTRA. 


if 

S 


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CO  m 


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II 
111 

118 
SBo 


s    a 
I   I 


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S3? 

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II! 


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ERBIUM   SALTS.  59 

the  field.    A  crystal  less  than  1  mm.  thick  in  a  field  of  2720  c.g.s.  units 
causes  a  difference  of  £  A  in  the  middle  of  some  bands. 

To  explain  the  Zeeman  effects  observed  we  must  consider  whether  the 
external  field  is  simply  added  to  the  intramolecular  fields,  or  whether  there 
are  variations  produced  there  by  the  presence  of  the  atoms.  If  one  assumes 
the  same  vibrators  in  every  case,  electrons  with  a  value  of  elm  of  1.8  (10)7, 
then  the  internal  magnetic  fields  must  vary  between  200,000  c.g.s.  units 
in  one  direction  and  about  the  same  number  of  units  in  the  opposite  direc- 
tion. Assuming,  on  the  other  hand,  that  the  intra-atomic  field  simply  has 
the  external  magnetic  field  added  then  Becquerel  gives  the  following  values 

of  e/m  =  2n  V  -&     jj,  +  referring  to  a  positive  electron: 

A  5206.5++,  e/m=  +4.5  (10)7;        A  5211.3++,  -0.3  (10)7; 

A5215.5++,  +2.1  (10)7;  A  5221.5  ++,  +1.6  (10)8; 

A  5225.6,  -1.4  (10)8;  A  5236.6++,  +  2.9  (10)7; 

A  5242.0+ +,  +1.9  (10)7;  A  5245.8++,  +4.5  (10)7; 

A  5251.1,  -7.1  (10)7;  A  6422.7,  -1.6  (10)8; 

X  6434.5,  - 1.4  (10)8;  A  6474.0,  +3.8  (10)7; 

A  6505.6+,  +5.1  (10)7;  A  6523.4++,  -5.9  (10)7; 

A  6537.0+,  -2.8  (10)7;  A  6542.5,  +3.4  (10)7; 

A  6564.4+,  -8.6  (10)7;  A  6581.0+,  +3.6  (10) 7. 

For  convenience  we  will  consider  that  some  of  the  above  bands  are 
due  to  +  electrons,  and  some  due  to  —  electrons,  according  to  the  value 
of  e/m  as  calculated  from  the  above  formula. 

The  magnetic  rotatory  polarization  is  very  closely  related  to  the  Zee- 
man effect,  the  +  and  —  electrons  behaving  differently  in  this  case  also;  the 
sense  of  the  rotation  being  different  for  the  +  and  for  the  —  electrons. 

J.  Becquerel,  in  Le  Radium,  March,  1907,  gives  a  theory  for  the  mag- 
netic optical  effects  which  are  observed  in  crystals.  The  general  basis  of  his 
theory  is  somewhat  similar  to  that  of  Voigt.1  The  electrons  are  considered 
to  move  along  each  coordinate  axis  independently.  The  three  directions  are 
considered  to  be  the  same  for  each  electron  and  independent  of  the  period 
of  the  exciting  light.  The  form  of  the  equations  is  then  similar  to  those  of 
a  pendulum  experiencing  great  frictional  resistance.  The  theory  as  here 
developed  explains  some  but  not  all  of  the  different  types  of  resolution  found 
experimentally.  As  different  results  have  been  obtained,  especially  by 
Page,2  the  development  given  by  Becquerel  will  not  be  considered  in  detail. 

Later  papers  by  Becquerel3  deal  with  the  effect  of  a  magnetic  field 
on  the  absorption  spectra  of  certain  crystals  of  xenotine,  tysonite,  parisite, 
monazite,  apatite,  and  zircon  at  low  temperatures.  The  bands  in  general 
are  displaced  towards  the  violet,  especially  for  tysonite,  as  the  tempera- 
ture is  lowered.  Many  changes  of  relative  intensity  occur  and  at  low 
temperatures  the  bands  are  invariably  narrower  and  more  intense. 

1  Ann.  Phys.,  6,  346  (1899);  6,  784  (1901);  8,  872  (1902). 
7  Trans.  Camb.  Phil.  Soc.,  vol.  20,  No.  13,  291,  322. 

•Compt.  rend.,  Feb.  25,  Mar.  25,  May  13,  June  17,  Aug.  19  (1907);  Le  Radium, 
Sept.  (1907). 


60 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


For  xenotine  the  following  table  is  given: 


Ordinary  spectra. 

E 

xtraordinary  spectra. 

A  at  25°. 

Displacement  between 
26°  and  -188°. 

A  at  25°. 

Displacement  between 
25°  and  -188°. 

5206.5 
5211  3 

Doubled,  0.4  to  violet  
1  5  to  violet  

5206.7 
5220  1 

0.4  to  violet. 
1  5  to  violet. 

5215  5 

0  5  to  violet  

5221  6 

0  1  to  violet  

5236  6 

05  to  red  

52372 

0  5  to  red 

52420 

0  9  to  red  

5251.1 

0  6  to  red 

52458 

0  5  to  red  

5251  1 

0  6  to  red  .  . 

5268 

0  4  to  violet 

There  does  not  seem  to  be  any  relation  between  the  Zeeman  effect  and 
the  effect  due  to  change  in  temperature.  Becquerel  also  states  that  the 
Zeeman  effect  is  independent  of  the  temperature.  Related  bands  are 
usually  affected  in  the  same  way  by  change  in  temperature. 

In  the  introduction  the  ordinary  equation  of  an  electron  considered 
in  the  theory  of  dispersion  was: 

=  eE  cos  pt 


The  resistance  KX  designates  a  mean  resistance,  and  causes  the  decay 
of  the  light  vibration.  It  may  result  from  sudden  shocks  undergone  in 
any  irregular  or  fortuitous  manner  by  any  of  the  electrons  taking  part  in 
the  absorption  of  light.  The  greater  K  is  the  wider  the  band  will  be.  The 
above  equation  leads  to  a  value  of  the  refractive  index  //. 


K  is  the  coefficient  of  absorption;  2  it  d0h  is  the  period  corresponding  to  the 
middle  of  an  absorption  band  h]  eh  is  a  coefficient  depending  on  the  sub- 
stance and  the  band. 


Ch'- 


Nh  is  the  number  of  electrons  h/cc.;   dlh  =  —  do*.    Becquerel  has  ob- 

mh 

tained  the  value  of  the  ratio  of  dl  at  20°  and  at  — 186°.     The  bands  are 
those  of  tysonite. 


A  at  20°. 

Ratio  of  «'. 

4791  spec,  extraord  
5176  spec  ord  .  . 

1.83 

1  84 

5235  spec  ord 

1  83 

1  85 

The  ratios  of  d'  are  very  nearly  the  same  as  the  ratios  of  the  square 
roots  of  the  absolute  temperature.     The  width  of  the  bands  measured 


ERBIUM    SALTS. 


61 


between  the  maxima  of  the  deviations  of  the  dispersion  curve  vary  directly 
as  the  square  root  of  the  absolute  temperature. 

If  this  law  is  true  then  the  size  of  the  bands  is  proportional  to  the 
mean  speed  of  translation  of  the  molecules.  Schonrock  l  has  shown  that 
the  width  of  bands  in  a  gas  results  not  only  from  the  Ddppler  effect  due  to 
the  kinetic  motion  of  the  gas  molecules,  but  also  from  collisions.  Colli- 
sions determine  the  sudden  and  fortuitous  variations  in  the  phase,  amplitude, 
and  direction  of  motion  of  the  electrons,  and  prevent  the  light  that  is  being 
emitted  or  absorbed  from  being  homogeneous.  The  size  of  the  bands  is 
then  a  function  of  the  mean  length  of  the  wave-trains  emitted  between 
collisions.  If  d  is  the  width  of  the  band  between  the  positions  where  the 
intensity  of  light  is  half  the  maximum,  and  r  is  the  length  of  the  train  of 
waves  emitted  between  collisions,  then: 


TIT 


nvL 


u  is  the  mean  speed  of  translation,  L  the  mean  free  path,  v  the  velocity  of 
light,  A  is  a  constant,  Mthe  molecular  weight,  T  the  absolute  temperature; 
L  =  1 2/p  2 1/27T,  I  is  the  mean  distance  between  the  centers  of  molecules; 
p  is  the  distance  between  two  molecules  at  the  time  of  their  collision. 

If  the  same  mass  and  volume  of  a  vapor  has  its  temperature  raised,  I 
and  p  are  but  slightly  changed,  so  that  the  width  of  the  bands  should  vary 
as  the  square  root  of  the  absolute  temperature.  The  above  theory  applies 
to  a  gas.  The  width  of  the  bands  of  solids  can  not  be  explained  on  the 
Doppler-Fizean  principle,  but  may  be  due  to  the  extremely  numerous 
shocks  of  the  molecules.  The  fineness  of  the  erbium  bands  may  then  be  due 
to  the  union  of  several  atoms  into  big  molecules  having  a  very  small  velocity 
of  translation.  If  the  molecules  are  large  the  collisions  will  be  less  numerous. 

In  a  later  paper  Becquerel 2  gives  some  values  for  the  terms  which 
appear  in  his  equation  giving  the  refractive  index.  It  should  be  stated 
here  that  dispersion  equations  differ  considerably  according  to  the  assump- 
tions made  in  their  calculation. 

TYSONITE. 


A  at  25°. 

Ih  at  25°. 

Wat  -188° 

4791 
5176 
5235 
5825 

2.29  (10)~T 
2.14  (10)~7 
.71  (10)~7 
4.82  (10)~7 

7.23  (10)-7 
5.31  (10)-7 
1.53  (19)~T 
2.35  (10)-7 

From  the  changes  of  Ih,  the  dielectric  coefficient,  with  changes  in  tem- 
perature, Becquerel  considers  that  the  increase  in  intensity  of  the  bands 
when  the  temperature  is  lowered  is  not  only  due  to  a  narrowing  of  the 
bands,  but  also  to  an  increase  in  the  total  amount  of  energy  absorbed  as 
the  dielectric  constant  is  increased.  Let  us  assume  that  e  =  3.4  (10)~10. 


Ann.  Phys.,  20,  995  (1906);  22,  210  (1907). 
Le  Radium,  Nov.  (1907). 


62 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 
TYSONITE 


A  8176. 

A  5235. 

e/m        

+  2.49 
1.01 
2.50 
4.05 
1.00 
0.89 
2.21 

10)7 
10)-' 

io)-» 

10)-13 
10)-" 
,10)" 
(10)l» 

—2.48  (10)' 
3.28  (10)-« 
7.07  (10)~« 
1.32  (10)->8 
2.85  (10)-'8 
2.9    (10)u 
6.25  (10)u 

#eat25°U.E.M  

Ne  at  —188°  
Nm&t  25°  

Nm  at  —188° 

AT  at  25°  

N  &t  —188°  

From  the  above,  then,  N,  the  number  of  absorbing  electrons  increases 
as  the  temperature  is  lowered.  The  number  of  absorbing  electrons  is  very 
much  smaller  than  the  number  of  atoms  present.  Hallo1  and  others  have 
shown  that  only  a  small  number  of  sodium  atoms  take  part  in  the  absorp- 
tion of  the  two  D  lines. 

Dt  (Hallo) e0  =  7.5(10)-"          N0f       =3.3    (10)1* 

A  (Gerst) e0i  =2.1  (10)-7         N0l        =1.1    (10)I§ 

A  5221.5  (Xenotine) . . .  .erf         =5.43  (10)-"         Nrf      =3.34  (10)18 
e— 188°  =  9.68  (lO)"8         N— 188  =  5.96  (10)18 

The  index  of  refraction  of  solids,  and  especially  minerals,  changes  very 
little  with  change  in  temperature,  so  that  the  electrons  influencing  refrac- 
tion are  but  slightly  affected  by  changes  in  temperature.  Drude,  Cheve- 
neau,2  and  others  have  shown  that  the  number  of  these  electrons  vibrating 
in  the  ultra-violet  is  approximately  that  of  the  valencies  of  the  atoms 
composing  the  molecule. 

Becquerel 8  has  continued  his  work  at  low  temperatures,  doing  part 
of  the  work  with  Onnes  4  at  Leyden.  One  of  the  problems  arising  from 
Becquerel's  work  is  whether  the  paramagnetism  of  erbium  and  neodymium 
affects  the  internal  magnetic  fields  which  would  exist  within  the  crystals 
if  they  were  diamagnetic.  For  this  reason  the  Zeeman  effect  is  found  for 
widely  different  temperatures.  If  the  Zeeman  effect  is  independent  of 
temperature  then  one  would  consider  that  paramagnetism  did  not  play  a 
very  important  r61e.  Becquerel  finds  the  Zeeman  effect  on  the  bands  of 
xenotine  and  tysonite  to  be  independent  of  the  temperature. 

In  a  table  giving  the  Zeeman  effect  on  tysonite  and  parisite  it  is  seen 
that  bands  that  are  in  practically  the  same  portion  of  the  spectrum  are 
affected  in  a  very  different  way  by  the  magnetic  field.  From  the  Zeeman 
effect  the  following  erbium  alcohol  bands  are  due  respectively:  ^  4870  to  — ; 
^  4880  to  -  ;  ^  5238  to  + ;  and  >l  5410  to  -  electrons. 

Considerable  data  are  given  by  Becquerel  upon  the  rotatory  magnetic 
polarization.  The  results  confirm  the  theory  of  the  Hall  effect — that  the 
sense  of  the  dispersion  is  just  the  opposite  on  the  outside  of  the  band  from 
what  it  is  on  the  inside.  Applying  the  theory  to  the  band  X  5221.5  of 
xenotine,  Becquerel  obtains  the  results  shown  in  the  following  table: 

1  Arch.  NSerlandaises  (2),  t.  10,  p.  148  (1905). 

2  Le  Radium,  June  (1907). 

1  Ibid.,  Jan.  (1908);  Nov.  (1909);  Compt.  rend.,  Dec.  9,  30  (1907). 
*Ibid.,  Aug.  (1908). 


ERBIUM   SALTS. 


63 


H. 

e/m. 

*e. 

*m. 

N. 

Temperature  20° 

14  100 

1  656  (10)8 

3  78  (10)~7 

2  28  (10)~18 

3.34  (10)13 

Temperature  —188°  .... 

12,300 

L656  (10)" 

6.74  (10)-' 

4.07  (10)~1S 

5.96  (10)" 

ERBIUM  CHLORIDE  IN  GLYCEROL. 

Several  photographs  (Plate  29,  A  and  B)  were  made  of  the  absorption 
spectra  of  erbium  chloride  dissolved  in  glycerol.  The  absorption  is  very 
similar  to  that  of  an  aqueous  solution;  the  bands,  however,  in  general  being 
shifted  towards  the  red.  The  bands  shown  by  a  solution  30  mm.  in  depth 
are  located  as  follows:  X  3250;  X  3370;  X  3510.  These  three  bands  are  quite 
strong,  being  some  30  or  40  Angstrom  units  wide;  X  3600  is  weak  and  narrow; 
X  3650  is  quite  strong;  X  3785  is  quite  strong;  >l  3885  is  considerably  weaker 
than  the  five  other  ultra-violet  bands  described  above;  X  4165;  X  4490  and 
X  4520  are  of  about  equal  intensity  and  quite  strong  (in  the  region  near  these 
bands  there  are  numerous  weak  bands  and  these  would  come  out  better  if 
a  greater  depth  of  cell  could  have  been  used,  but  on  account  of  the  slight 
solubility  of  erbium  chloride  in  glycerol  the  use  of  a  greater  cell-depth  was 
not  practicable);  X  4910  weak;  X  5190;  >l  5210;  X  5225  rather  strong;  X  5240 
weak;  X  5260  weak;  X  5380;  >l  5420;  X  5440;  X  6450;  and  X  6530.  The  meas- 
urements were  from  a  spark-line  at  X  3995  and  hence  are  more  accurate 
in  this  region.  On  the  whole,  most  of  the  erbium  chloride  bands  are  of 
greater  wave-length  for  the  glycerol  solution  than  for  the  aqueous  solution. 

The  relative  intensities  of  the  water  and  glycerol  bands  differ  consider- 
ably, but  the  wave-lengths  do  not  appear  to  be  very  greatly  changed.  The 
photographic  films  appear  to  have  contracted  differently  on  drying,  so  that 
no  very  accurate  comparisons  of  the  wave-lengths  of  the  water  and  glycerol 
bands  could  be  made. 

Rise  in  temperature  from  15°  to  200°  produces  no  noticeable  change 
in  wave-length.  At  the  higher  temperature  the  bands  are  very  much  less 
distinct  and  apparently  considerably  weaker.  For  instance,  the  group  of 
bands  at  15°  at  X  5200  practically  becomes  a  single  haay  band  at  200°. 

ERBIUM  CHLORIDE  IN  WATER,  EFFECT  OF  TEMPERATURE. 

A  spectrogram  (Plate  30,  B)  was  made  to  show  the  effect  of  rise  in 
temperature  on  the  absorption  spectrum  of  an  aqueous  solution  of  erbium 
chloride.  For  this  purpose  a  0.94  normal  solution  was  used  and  the  depth 
of  layer  was  48  mm.  The  solution  probably  contained  a  considerable 
number  of  impurities,  so  that  the  amount  of  erbium  was  in  fact  quite  small. 
The  absorption  spectrum  was  found  to  change  but  little  with  rise  in  tem- 
perature, thus  indicating  a  dilute  solution.  Exposures  were  made  for  30 
seconds  to  the  Nernst  glower  and  4  minutes  to  the  spark.  The  current 
through  the  glower  was  0.8  ampere  and  the  slit-width  0.20  mm.  Starting 
with  the  spectrum  nearest  the  comparison  scale,  the  temperatures  were 
7°,  17°,  29°,  46°,  60°,  70°,  and  80°. 

At  70°  the  ultra-violet  is  absorbed  to  X  3950.  As  the  temperature  is 
raised  the  ultra-violet  absorption  increases,  and  at  80°  it  reaches  X  3150. 


A   STUDY   OF   THE   ABSORPTION    SPECTRA. 


Bands  from  20  to  40  Angstrom  units  wide  occur  at  A  3235, 1  3510,  ^  3640  and 
4  3785.  These  bands  are  slightly  wider  at  80°,  but  as  for  all  the  other 
erbium  bands  this  widening  is  very  small.  Weak  and  narrow  bands  appear 
at  >U  4165,  4425,  4458,  4500  (strong),  4535,  4540,  4555,  4580,  4685,  4750 
(30  Angstrom  units  wide),  4810,  4840,  4855,  4870  (strong  and  20  Angstrom 
units  wide),  and  4920.  A  4920  lies  alongside  of  a  fuzzy  band  extending 
from  /I  4910  to  X  4950. 

After  these  comes  a  rather  wide  band  which  for  a  shorter  length  of 
layer  would  most  likely  be  broken  up  into  a  number  of  much  finer  bands. 
This  band  extends  from  I  5190  to  I  5250.  At  A  5217  a  narrow,  sharp  line 
runs  through  the  fuzzier  and  wider  band.  Broad  (about  30  Angstrom 
units  wide)  and  very  faint  bands  are  located  at  X  5630  and  A  5760.  For 
greater  concentrations  these  would  probably  show  as  finer  bands.  The 
band  at  ^  6540  is  much  more  diffuse  on  the  red  than  on  the  violet  side; 
this  possibly  being  due  to  a  component  that  is  not  separated  at  this  tempera- 
ture. Other  bands  are  located  at  M  5365,  5380,  5425,  5445,  5505,  6410, 
6440,  6495,  and  6690.  The  general  effect  of  rise  in  temperature  here  is  to 
cause  the  lines  to  become  slightly  fuzzier  and  to  show  more  of  a  "  washed- 
out"  appearance.  No  shift  or  rise  in  temperature  was  noticed. 

ADSORPTION  SPECTRA  OF  ERBIUM  NITRATE  AND  OTHER  SALTS  OF  ERBIUM. 

It  was  thought  to  be  of  interest  to  test  whether  the  N03  group  had  any 
hypsochromous  effect  on  the  absorption  spectra  of  aqueous  solutions  of 
erbium  salts.  The  following  approximate  wave-lengths  of  the  bands  do  not 
show  any  such  hypsochromous  effect  as  was  found  for  the  uranyl  bands: 


Erbium 
nitrate. 

Erbium 
chloride. 

Erbium 
nitrate. 

Erbium 
chloride. 

Erbium 
nitrate. 

Erbium 
chloride. 

3630 

3635 

4270$ 

5210 

5205 

3760* 

4425 

4415 

5235 

5230 

3788f 

3785 

4480§ 

5365 

5365 

3880J 

4500 

4905 

5420 

5415 

4045 

4675§ 

4670§ 

6400 

6410 

4070 

4730§ 

6480 

6490 

4160 

4150 

4850 

4845 

6530 

6535 

4190 

4870 

4865 

4215 

4210 

4910§ 

4905 

*Hazy.       t  Strong.       I  Wide  and  weak.       gWeak. 

The  crystals  of  erbium  sulphate  have  a  fine  absorption  spectra.  As 
the  water  of  crystallization  is  driven  off  the  bands  change  very  consider- 
ably and  become  much  more  diffuse.  The  reflection  spectrum  from  fused 
erbium  oxide  consists  of  a  large  number  of  fine  lines.  As  shown  by  Ander- 
son, these  lines  become  wider  as  the  temperature  is  raised,  until  they 
become  emission  bands.  The  emission  bands  are  quite  broad.  Between 
100°  and  600°  some  of  the  fine  erbium  bands  shift  about  10  Angstrom 
units.  The  difference  between  the  wave-lengths  of  the  emission  bands  and 
the  absorption  bands  at  high  temperatures  is  hidden  by  the  haziness  of  the 
bands  if  it  exists  at  all. 


CHAPTER  IX. 

PRASEODYMIUM  SALTS. 

Introduction. — Praseodymium  chloride. — Praseodymium  nitrate. 
INTRODUCTION. 

Very  little  work  has  been  done  upon  praseodymium  compounds,  for 
the  reason  that  the  absorption  bands  are  much  wider  than  those  of  erbium 
or  neodymium.  Bois  and  Elias  have  worked  on  Pr2(SO4)38H2O.  At 
-190°  they  found  bands  at  AA  5990  to  5993  and  AA  6009  to  6014.  These 
bands  broadened  slightly  when  a  magnetic  field  of  40,000  c.g.s.  units  was 
applied.  The  widening  was  much  less  than  that  obtained  by  Becquerel  for 
neodymium  bands. 

Jones  and  Anderson  found  that  the  ultra-violet  band  A  3000  was  a 
"methyl  alcohol"  band  and  was  very  weak  for  aqueous  solutions,  if  it 
existed  at  all.  They  think  that  there  are  other  "alcohol  "  bands,  but  that 
they  are  not  far  enough  separated  from  the  "water"  bands  to  appear  by 
themselves.  Similar  results  are  found  in  the  region  A  5900. 

PRASEODYMIUM  CHLORIDE. 

A  spectrogram  (Plate  31,  A)  was  made  of  a  2.56  normal  aqueous 
solution  of  praseodymium  chloride  3  mm.  deep.  Exposures  were  made  to 
the  Nernst  glower  (current  0.8  ampere  and  slit-width  0.20  mm.)  for  20 
seconds.  The  time  of  exposure  to  the  spark  was  4  minutes.  Starting  with 
the  strip  nearest  the  numbered  scale,  the  temperatures  were  7°,  23°,  40°, 
52°,  68°,  and  84°. 

The  ultra-violet  is  absorbed  up  to  A  2700  and  this  absorption  does  not 
vary  greatly  with  temperature,  increasing  slightly,  however.  At  7°  there 
are  bands  from  A  4385  to  A  4500,  A  4640  to  A  4720,  A  4810  to  A  4845,  A  6860 
to  A  6990.  This  latter  band  is  double,  the  red  component  being  much  the 
narrower  and  having  its  center  at  A  6980.  Throughout  the  remainder  of 
the  spectrum  there  is  complete  transmission. 

At  84°  the  absorption  bands  are  located  at  AA  4380  and  4510,  AA  4640 
and  4730,  AA  4810  and  4845,  and  AA  6870  and  6775.  The  bands  all  widen 
slightly  except  the  latter.  At  7°  the  latter  band  consisted  of  two  separate 
bands.  At  84°  the  A  6980  band  has  diffused  into  the  other  band  and  the 
general  transmission  throughout  the  band  has  been  greatly  increased.  In 
this  respect  this  band  is  very  peculiar  indeed,  and  behaves  with  respect 
to  temperature  changes  in  just  the  opposite  way  from  practically  all  other 
bands  investigated. 

A  spectrogram  (Plate  31,  E)  was  made  of  a  0.043  normal  aqueous  solu- 
tion of  praseodymium  chloride  196  mm.  deep.  This  spectrogram  was  to  show 
whether  changes  due  to  temperature  in  the  spectrogram  were  affected  by  the 
concentration  of  the  solution.  The  length  of  exposures  to  the  Nernst  glower 
(current  0.8  ampere  and  slit-width  0.20  mm.)  was  20  seconds.  The  length  of 
5  65 


66  A    STUDY   OP   THE   ABSORPTION    SPECTRA. 

exposure  to  the  spark  was  4  minutes.  Starting  with  the  strip  nearest  the 
comparison  spectrum,  the  temperatures  were  7°,  20°,  36°,  51°,  66°,  and  82°. 

The  absorption  spectrum  of  the  dilute  solution  is  practically  the  same 
as  that  for  the  concentrated  solution.  At  7°  bands  occur  from  A  4385  to 
A  4490,  A  4640  to  A  4715,  A  4810  to  A  4840,  A  5860  to  X  5940'  and  a  narrow 
band  at  A  5980. 

The  ultra-violet  absorption  at  7°  extends  to  A  2650;  at  82°  it  extends 
to  X  2750.  The  other  bands  are  at  AA  4385,  4490,  4650,  4715,  AA  4805  to 
4835,  AA  5870  to  5930.  The  band  A  5980  has  become  much  more  diffuse. 
The  band  adjacent  to  it  has  also  become  narrower  and  much  more  filled  up 
by  general  transmission  than  at  the  lower  temperatures.  It  will  be  seen 
in  general  that  there  is  very  little  if  any  temperature  change  in  the  ab- 
sorption bands  of  praseodymium  chloride  at  this  concentration,  except  the 
bands  in  the  red,  which  become  narrower  and  weaker  at  the  higher  temper- 
atures. In  the  concentrated  solution  the  change  in  this  band  was  not  as 
great  as  in  the  dilute  solution.  In  the  concentrated  solutions  the  other 
bands  widened  slightly  more  than  they  do  in  the  solution  here  described. 

The  spectrogram  (Plate  32,  B)  of  an  aqueous  solution  of  praseody- 
mium chloride  shows  the  effect  of  change  in  temperature  between  7°  and  84° 
on  a  2.56  normal  solution  48  mm.  deep.  The  exposure  to  the  Nernst  glower 
(current  0.8  ampere  and  slit-width  0.20  mm.)  was  for  20  seconds.  The  ex- 
posure to  the  spark  was  for  4  minutes.  Starting  from  the  comparison  spec- 
trum, the  strips  were  taken  at  the  temperatures  7°,  20°,  35°,  51°,  66°,  and  84°. 

The  spectrum-strip  at  7°  shows  a  large  band  in  the  blue  and  one  in  the 
yellow.  There  is  absorption  in  the  ultra-violet.  In  the  case  of  praseo- 
dymium nitrate  the  absorption  in  the  ultra-violet  was  probably  due  to  the 
NO,  band.  This  absorption  was  found  to  be  unaffected  by  temperature. 
In  the  case  of  praseodymium  chloride  the  absorption  increases  very 
markedly  with  rise  in  temperature.  At  7°  the  limits  of  the  blue  band  are 

4270  }  and  {  4930  }  and  for  the  yellow  band  ^  575°  and  610°- 
There  is  slight  absorption  in  the  region  X  5000  to  X  5100,  which  is  prob- 
ably due  to  absorption  bands.  Two  fine  bands,  each  about  8  Angstrom 
units  wide,  appear  at  XX  5220  and  5235.  Absorption  of  the  shorter  wave- 
lengths at  7°  is  complete  to.  A  3100,  at  51°  A  3200,  and  at  84°  A  3300.  At 
51°  the  blue  band  is  located  at  AA  4280  and  4950,  and  the  yellow  band  at 
AA5740  and  6110. 

At  84°  the  limits  of  the  blue  band  are  AA  4280  and  4950,  and  of  the 
yellow  band  AA  5750  and  6110.  The  widening  of  the  bands  is  very  small 
indeed.  The  fine  bands  AA  5220  and  5235  become  much  more  diffuse  and 
at  the  higher  temperatures  could  not  be  resolved  at  all.  At  7°,  however, 
the  two  bands  were  entirely  separated.  The  blue  and  yellow  bands  are 
very  slightly  affected  by  temperature  within  the  ranges  investigated. 

PKASEODYMITJM  NITRATE. 

A  spectrogram  (Plate  32,  A)  showing  the  effect  of  rise  in  temperature 
was  made  for  a  2.6  normal  aqueous  solution  of  praseodymium  nitrate  46.5 
mm.  deep.  The  exposures  were  made  to  the  Nernst  glower  (current  0.8 


PRASEODYMIUM   SALTS.  67 

ampere  and  slit-width  0.20  mm.)  for  20  seconds.  The  length  of  exposure 
to  the  spark  was  4  minutes.  Starting  with  the  strip  nearest  the  compari- 
son scale,  the  temperatures  were  6°,  19°,  47°,  70°  and  90°. 

On  account  of  the  great  concentration  and  the  depth  of  cell,  the  absorp- 
tion bands  are  very  wide.  The  whole  ultra-violet  portion  of  the  spectrum 
is  absorbed  up  to  X  3550.  Rise  in  temperature  does  not  cause  any  change 
in  this  absorption.  The  band  in  the  blue  extends  from  X  4300  to  X  4940  at 
6°.  A  weak  and  rather  broad  band  appears  at  X  5120  and  a  narrow  band  at 
X  5240,  this  band  being  about  15  Angstrom  units  wide.  The  yellow  band 
extends  from  X  5760  to  X  6120  at  6°. 

As  the  temperature  rises  the  blue  and  yellow  bands  gradually  widen. 
At  47°  the  blue  band  extends  from  X  4290  to  X  4950,  the  yellow  band  from 
X  5750  to  X  6120.  At  90°  the  violet  band  was  bounded  by  XX  4280  and  4960, 
the  yellow  band  by  XX  5740  and  6140.  At  70°  the  ballast  burned  and  the 
exposure  to  the  Nernst  glower  was  not  quite  as  long  as  it  should  have  been. 

The  bands  XX  5120  and  5240  appeared  very  slightly  affected  by  the  rise 
in  temperature  here  used.  The  violet  and  yellow  bands  broadened  very 
slightly  and  symmetrically  with  rise  in  temperature. 

Plate  33,  A,  represents  the  absorption  spectra  of  a  2.6  normal  solution 
of  praseodymium  nitrate  3  mm.  deep.  Starting  with  the  strip  nearest  the 
numbered  scale,  the  temperatures  are  6°,  16°,  34°,  46°,  58°,  70°,  and  82°. 

The  four  characteristic  wide  absorption  bands  appear  very  slightly 
affected  by  rise  in  temperature.  The  NO,  band  in  the  ultra-violet  widens 
slightly. 


CHAPTER  X. 


NEODYMIUM    SALTS. 

Introduction. — Neodymium  salts  in  aqueous  solutions. — Neodymium  salts  in 
glycerol. — Neodymium  nitrate  in  nitric  acid. — Spectrophotography  of  the 
chemical  reactions  in  which  neodymium  salts  take  part. — Summary. 

INTRODUCTION. 

J.  Becquerel  has  carried  out  investigations  on  several  neodymium  com- 
pounds similar  to  those  on  erbium.  Tysonite  was  especially  studied.  This  is 
a  fluoride  of  cerium,  lanthanum,  and  didymium  and  gives  mainly  the  didym- 
ium  spectrum.  The  bands  >U  5176+ +,  5234++,  6250  (doubles  4.5  unsym.), 
6740,  6742+,  and  6760+  were  found  to  broaden  in  the  magnetic  field.  Em- 
ploying the  usual  theory  of  the  Zeeman  effect,  Becquerel  shows  that  X  3995 
is  due  to  +  electrons;  X 5075+  to  +  electrons;  X 5 109+  to— electrons;  1 5176+  + 
to  +  electrons;  A  5234  +  +  to  -  electrons,  and  X  7642+  to  -  electrons. 

At  - 180°  the  bands  are  much  finer.  The  band  A  6249.7  is  very  fine 
and  from  the  Zeeman  effect  it  appears  to  be  due  to  +  and  —  electrons. 
The  following  table  gives  some  of  Becquerel's  results: 


Tysonite. 

Parisite. 

A  at  -188°. 

A*H  =  15000 

e/m-'-rv^ 

A  at  -188°. 

AA 

c/m 

3996      * 

0.8 

+   6.3  (10)7 

4274.  8/ 

0.20 

-   1.38(10)' 

4259.  8  sand/ 

0.1 

-  0.7  (10)7 

4724.  7/ 

0.42 

+  2.37(10  7 

4268      s  and/ 

0.1 

+  0.7  (10)7 

4747.0 

0.40 

-   2.  20(10  7 

4721.  4  sand/ 

0.1 

-  0.6  (10)7 

5095.  7  8 

2.39 

+  11.56(10  7 

5064.  4/ 

0.4 

+  2.0  (10)7 

5186.0s 

0.37 

+   1.  73(10  7 

5073.  5/ 

1.1 

+  5.32(10)7 

5208.0s 

0.37 

-   1.  71(10  7 

5079.  If 

0.54 

-  2.63(10)7 

5220.0s 

0.18 

+  0.83(10  7 

5087.  2/ 

0.99 

-  4.81(10)7 

5231.0s 

0.27 

+   1.24(10)7 

5098 

0.33 

+   1.0  (10)7 

5256.0 

0.60 

-  2.70(10)7 

5110 

0.92 

-  4.4  (10)7 

5685.0 

1.00 

+  3.90(10)7 

5173s 

0.53 

+  2.5  (10)7 

6232.7 

0.77 

-  2.40(10)7 

5185.  7  sand/ 

0.27 

+   1.26(10)7 

6239.6 

1.14 

-  3.70(10)7 

5220     s  and/ 

0.14 

-  0.64(10)7 

6246.9 

0.60 

-   1.90(10)7 

5234.  6  sand/ 

0.54 

-  2.48(10)7 

6723.0 

0.90 

-  2.50(10)7 

6224.  9  / 

0.4 

+   1.2  (10)7 

6735.0 

0.90 

-  2.50(10)7 

6234.  8  / 

0.5 

-   1.6  (10)7 

6746.0 

0.90 

-  2.60(10)7 

6242.  6/ 

1.2 

-  3.90(10)7 

6249.  7  sand/ 

3.27 

±10.52(10)7 

6267     / 

0.4 

+   1.30(10)7 

6683 

1.86 

-  5.23(10)7 

6740 

0.86 

-  2.38(10)7 

6761 

0.41 

-   1.13(10)7 

The  series  of  acetate  bands  is  very  much  like  that  of  the  uranyl  series, 
except  that  it  runs  in  the  opposite  direction.  The  absorption  spectra  of 
uranous  bromide  in  glycerol  and  in  methyl  alcohol  are  also  similar. 


70  A    STUDY   OF   THE   ABSORPTION    SPECTRA. 

The  foregoing  table  shows  that  the  Zeeman  effect  on  related  bands  of 
tysonite  and  parisite  is  very  different  (parisite  is  a  carbonate  of  the  didym- 
ium  group).  An  examination  was  made  on  yellow  Spanish  apatite,  a  flour- 
phosphate  of  calcium  and  didymium.  The  apatite  bands  are  quite  broad. 
The  band  >l  5270  gave  a  circular  vibration  indicating  +  electrons,  A  5750  + 
electrons,  >l  5820  +  electrons,  and  ^  5860  —  electrons. 

A  solution  of  needy mium  nitrate  in  ethyl  alcohol  has  also  been  tried. 
The  bands  M  5229,  5219,  and  5239  were  broken  into  two  components  by  the 
magnetic  field,  the  amount  being  0.5  Angstrom  unit  for  H  =  14,000  c.g.s. 
units.  The  sense  of  the  polarization  indicated— electrons.  The  bands 
>U  5815  and  5831  are  affected  but  little  and  indicate  +  electrons.  The  effect 
of  the  magnetic  field  seems  to  be  independent  of  the  solvent.  The  addition 
of  perchloride  of  iron  had  no  effect.  The  spectrum  was  observed  as  the 
solution  was  warmed  so  as  to  change  the  solid  alcohol  to  liquid  alcohol. 
No  discontinuous  change  in  the  spectrum  was  noticed. 

Neodymium  chloride  in  alcohol  (methyl)  has  a  sensitive  band  at  ^  5096 
giving  a  separation  of  1.1  Angstrom  units  for  H=  14,000.  The  sense  in- 
dicates a  -f-  electron.  A  5207  gives  a  separation  of  0.4  having  a  —  sense, 
A  5220  a  separation  of  0.4  in  a  —  sense,  while  ^  5225  does  not  show  any 
effect.  The  bands  U  5761  (0.4,+ electrons),  5787  (0.4, -electrons),  5796 
(  —  electrons),  and  the  two  bands  at  6800  (—electrons)  gave  measurable 
Zeeman  effects.  No  difference  was  found  between  "  water  "  and  "  alcohol  " 
bands. 

The  addition  of  small  amounts  of  the  nitrate  of  neodymium  to  the  chlo- 
ride in  an  alcoholic  solution  rapidly  causes  the  disappearance  of  the  bands 
M5207,  5225,  5727,  5745,  and  5761.  When  equal  amounts  of  the  two  salts 
are  present  these  bands  have  practically  disappeared.  The  band  ^  5220  re- 
mains. At  the  same  time  new  bands  appear  at  M5235,  5777,  5814,  and 
6229.  The  band  X  5229  is  due  to  - ,  >l  5235  to  - ,  and  A  5814  to  +  electrons. 

Becquerel  and  Onnes  l  continued  the  work  on  absorption  spectra  at 
temperatures  of  liquid  and  solid  hydrogen.  The  general  effect  of  cooling 
is  to  make  the  bands  more  intense  and  often  to  cause  new  bands  to  appear. 
The  reverse  action  very  seldom  occurs.  But  when  the  temperatures  of 
liquid  hydrogen  (20°  absolute)  or  solid  hydrogen  (14°  absolute)  are  reached 
it  is  found  that  many  bands  have  weakened,  or  even  disappeared.  The 
band  X  5235  of  tysonite  is  a  band  of  this  kind.  At  very  low  temperatures, 
then,  the  spectrum  is  much  simpler  than  at  higher  temperatures.  Some  of 
the  bands  even  pass  through  a  minimum  of  width.  The  band  ^5176  of 
tysonite  passes  through  a  minimum  between  20°  and  14°.  Becquerel 
suggests  that  there  should  be  a  relation  between  the  effect  of  temperature 
on  the  absorption  and  the  effect  of  temperature 2  on  electrical  resistance. 
At  very  low  temperatures  the  metals  should  be  transparent. 

The  effect  of  a  magnetic  field  on  the  absorption  bands  was  found  to  be 
independent  of  the  temperature,  and  this  fact  Becquerel  believes  is  a  strong 
argument  for  the  view  that  positive  electrons  exist  within  the  atoms. 

1  Le  Radium,  Aug.  (1908). 

1  Onnes:  Comm.  Leyden,  suppl.,  9,  25  (1904);   Onnes  and  Clay:   Comm.  Leyden, 
95,  99. 


NEODYMIUM   SALTS. 


71 


The  following  table  gives  the  wave-lengths  of  the  neodymium  bands 
in  aqueous  solution  as  measured  by  various  spectroscopists: 


BUhl. 

Demarcay  » 

Muthmann.* 

Drossbach.* 

Foesling.* 

For- 

manek.* 

Exner." 

A 
B 

C 

7420 

6900 
6810 
6710 

6360 
6280 
6240 
6220 

7324 

6910 
6804 
6731 

6373 
6292 

6234 

6892 
6798 
6720 

6360 
6285 
6250 
6215 

5834 

.  .. 

6895 
6775 
6720 

6360 
6278 
6254 
6217 

7291 

6906 
6794 

6235 

6750 

5808 

D 
E 

5790 
5750 

5720 

5330 
5240 
5210 

5783 

5320 
5220 

5785 
5754 
5735 
5716 

5323 
5254 
5216 
5205 

5880-5660 

5320 
5270-5190 

sieo 

5788-5780 
5754 
5735 
5716 

5323 

52i<3 
5204 

5797 
5759 

5319 

5222 
5209 

5795 
5740 

5235 
5i20 

5130 
5090 

5io9 

5120-5110 
5089 

4780 

5124 
5087 

4799 

5120 
5096 

4821 

4830 

G 
J 

4760 
4690 
4620 

4340 
4280 

4190 
3800 
3560 

4768 
4691 
4624 

435i 
4294 
4281 
4200 

4745 
4595' 

4340 
4325 
4273 

3803 

47i6 
4630 

4340 
4275 

3590 

4748-4742 
4687 
4610 

4330 
427i 

3804 

4759 
4695 
4614 

4443 
4341 

4271 

4760 
4700 
4620 

4430 
4270 

(' 

3540 
3500 
3470 

.... 

•  .  •  . 

3560 
3510 

3538 
3503 
3468 

3420 

3478 

M 

3390 
3290 

3370 
3280 

3350^-3130 

»Compt.  rend.,  126,  1039  (1898). 

*Ber.  d.  deutsch.  chem  Gesell.,  32  (1899). 

•Ibid..  35.486(1909). 


«  Ztschr.  anorg.  Chem..  118  (1907). 

'Die  qualitat.  Spectralanal.  anorg.  Kflrper,  Berlin  (1900). 

•Wiener  Sitzungsberichte,  1 18.  a  1252-1266  (1899). 


Stahl  states  that  the  bands  A  6950,  /I  6840,  and  A  6780  vary  enormously  in 
their  relative  intensities  in  the  various  solutions.  In  the  presence  of  strong 
nitric  acid  the  bands  ^  4710,  X  4690,  and  X  4570  disappear  completely.  The 
absorption  spectrum  of  the  chloride  is  independent  of  the  presence  of  free  acid. 

Neodymium:  /I  6710,  Jl  6240,  X  5790,  X  5720,  ;  4340,  A  4190,  .13800, 
A  3390,  X  3270. 

Praseodymium :    Jl  5970,  A  5890,  X  4820,  X  4690,  J  4440. 


72  A    STUDY    OF   THE    ABSORPTION   SPECTRA. 

The  A  4690  band  is  common  to  solutions  of  both  neodymium  and  pra- 
seodymium, and  this  has  led  some  to  believe  that  there  is  a  common  element 
in  these  two  substances.  Stahl  considers  the  view  that  there  are  several 
elements  in  neodymium  as  very  improbable. 

THE  EFFECT  OF  RISE  IN  TEMPERATURE  ON  THE  ABSORPTION  SPECTRA  OF  AQUEOUS 
SOLUTIONS  OF  NEODYMIUM  SALTS. 

A  spectrogram  (Plate  38,  A)  of  a  3.4  normal  solution  of  neodymium 
chloride  in  water,  43  mm.  deep,  was  taken.  The  exposures  were  made  for 
3  minutes  to  the  Nernst  glower,  the  current  being  0.8  ampere  and  slit- 
width  0.20  mm.  The  time  of  exposure  to  the  spark  was  6  minutes.  Start- 
ing with  the  strip  nearest  to  the  comparison  spectrum,  the  temperatures 
were  6°,  21°,  36°,  47°,  60°,  77°,  and  83°. 

Neodymium  chloride,  under  the  conditions  of  this  experiment,  gives 
a  complete  absorption  in  the  ultra-violet  up  to  A  3700.  From  X  3700  through- 
out the  violet  and  blue  regions  there  is  almost  complete  general  absorption, 
this  general  absorption  increasing  with  the  temperature.  A  band  of  ab- 
sorption seems  to  appear  at  about  A  4000,  but  this  is  somewhat  doubtful. 
A  very  sharp  and  strong  band  appears  at  A  4185.  A  band  occurs  at  A  4265 
to  A  4305  and  one  at  A  4320  to  X  4350.  The  transmission  band  between  these 
two  bands  is  faint  and  disappears  at  77°.  An  absorption  band  extends 
from  A  4380  to  A  4520  and  there  is  then  complete  absorption  up  to  A  4980. 
The  transmission  between  these  bands  is  very  weak  and  has  almost  dis- 
appeared at  83°.  Between  A  4970  and  X  5365  there  is  an  absorption  band, 
the  long  wave-length  edge  of  this  band  being  extremely  sharp.  A  similar 
band  lies  between  X  5620  and  A  6000.  Next  comes  a  series  of  five  absorption 
bands.  The  first  of  these  is  20  Angstrom  units  wide  and  is  at  X  6250, 
the  next  is  10  Angstrom  units  wide  and  is  at  X  6270.  The  bands  AA  6295 
and  6315  almost  touch  each  other,  the  distance  between  them  being  but 
two  or  three  Angstrom  units.  The  last  band  is  about  30  Angstrom  units 
in  width  and  its  center  lies  at  A  6380.  The  last  band  that  could  be  photo- 
graphed was  between  A  6720  and  X  6965. 

The  effect  of  rise  in  temperature  is  quite  evident,  most  of  the  bands 
widening  and  their  sharpness  gradually  decreasing.  At  83°  the  band 
X  4970  to  X  5365  described  above  has  widened  to  A  4960  and  A  5395,  the 
widening  being  slightly  greater  on  the  red  side.  The  band  A  5620  to  A  6000 
has  widened  to  AA  5610  and  6050,  this  widening  also  being  unsymmetrical. 
The  five  bands  in  the  vicinity  of  A  5800  at  6°  have  merged  into  three  bands. 
The  red  band  is  at  AA  6720  to  6990.  It  will  thus  be  seen  that  the  widening 
is  in  general  greater  on  the  red  side  of  the  bands. 

A  spectrogram  (Plate  37,  A)  of  the  absorption  spectrum  as  affected 
by  change  in  temperature  was  made  for  a  neodymium  chloride  solution 
in  water,  the  concentration  being  3.4  normal  and  the  depth  of  layer  12  mm. 
The  length  of  exposure  was  2  minutes  to  the  Nernst  glower  (current  0.8 
ampere  and  slit-width  0.20  mm.).  The  time  of  exposure  to  the  spark  was 
6  minutes.  Starting  with  the  strip  nearest  the  numbered  scale,  the  tem- 
peratures were  11°,  22°,  33°,  45°,  59°,  73°,  and  85°. 

At  11°  an  absorption  band  appears  at  about  A  2970,  a  very  strong  band 
from  A  3250  to  A  3285,  and  an  adjacent  band  from  A  3285  to  A  3310.  A  very 


NEODYMIUM   SALTS.  73 

narrow  and  feeble  transmission  band  separates  these  two  bands.  At  85° 
the  transmission  band  has  weakened  very  much.  At  11°  a  very  strong 
band  lies  between  >l  3490  and  A  3580.  The  band  A  4274  is  about  8  Angstrom 
units  wide.  An  extremely  narrow  band  appears  at  A  4297,  X  4306,  and  A  4324. 
At  A  4234  is  a  wider  and  rather  diffuse  band,  it  being  about  12  Angstrom 
units  wide.  Bands  lie  between  A  4415  and  A  4470,  A  4580  and  A  4650,  A  4665 
and  A  4710,  A  4740  and  A  4775,  A  4815  and  A  4835,  and  the  very  wide  bands 
AA  5010  and  5300  and  AA  5665  and  5935.  Weak  bands  are  located  at  A  4645, 
A  4800,  A  5320,  A  6235,  A  6255,  A  6280,  A  6305,  and  A  6380.  Rather  diffuse 
bands  appear  at  AA  6780  and  6840,  at  A  6850,  and  from  A  6870  to  A  6920. 

The  effect  of  rise  in  temperature  from  11°  to  85°  is  quite  noticeable, 
although  it  is  not  great.  In  the  ultra-violet  there  is  a  slight  increase  in  the 
general  absorption.  The  bands  AA  3285  and  3310  widen  slightly.  The  band 
AA  3490-3580  at  11°  has  widened  so  that  at  85°  it  extends  from  A  3450  to 
A 3600.  The  bands  at  AA4415  and  4470  have  widened  but  little.  The  bands 
from  A  4600  to  A  4800  have  also  widened  but  little.  The  faint  diffuse  bands 
AA  4645  and  4800  have  practically  disappeared.  The  bands  AA  5010  and 
5300  and  AA  5665  and  5935,  at  11°,  have  widened  at  85°  to  AA  5010  and 
5350  and  AA  5660  and  5985.  The  widening  of  the  latter  band  is  distinctly 
unsymmetrical.  The  existence  of  the  band  A  5320  causes  the  band  A  5010 
to  A  5300  to  widen  unsymmetrically. 

The  bands  in  the  region  A  6300  become  less  sharp  as  the  temperature 
rises.  At  11°  there  was  considerable  transmission  in  the  region  A  6850. 
At  85°,  however,  this  transmission  disappears  and  there  is  practically  com- 
plete absorption  from  A  6760  to  A  6920.  The  very  sharp  bands  AA  4282, 
4300,  4310,  4322,  and  4343  do  not  appear  to  change  very  much  with  change 
in  temperature.  On  the  strip  taken  at  73°  these  bands  appear  sharper  than 
on  any  of  the  other  strips. 

A  spectrogram  (Plate  37,  B)  showing  the  effect  of  rise  in  temperature 
was  made  on  a  0.17  normal  neodymium  chloride  solution  in  water  196 
mm.  deep.  The  amount  of  neodymium  chloride  in  the  path  of  the  light  is 
approximately  the  same  as  in  the  spectrogram  showing  the  effect  of  tem- 
perature on  a  3.4  normal  solution  in  a  cell  12  mm.  deep.  In  this  case  the 
temperatures  were  5°,  16°,  28°,  42°,  59°,  72°,  and  82°.  Exposures  were 
made  to  the  Nernst  glower  for  3  minutes  (current  0.8  ampere  and  slit- 
width  0.20  mm.).  Each  strip  was  exposed  to  the  spark  for  6  minutes. 
The  purpose  of  making  this  spectrogram  was  to  find  the  effect  of  concen- 
tration of  a  salt  upon  the  changes  produced  by  change  in  temperature. 

A  description  of  the  bands  at  5°  and  82°  will  be  given.  Any  change 
that  takes  place  between  these  two  temperatures  is  a  gradual  one.  Trans- 
mission begins  at  A  2600.  Bands  appear  between  A  3250  and  A  3300  and 
A  3455  and  A  3575.  The  band  A  4274  is  much  sharper  and  narrower  than 
for  the  more  concentrated  solution.  The  numerous  fine  bands  in  the  region 
A  4300  are  very  faint.  The  bands  A  4420  to  A  4460,  A  4600  to  A  4630,  A  4645, 
A  4680  to  A  4705,  A  4745  to  A  4770,  and  A  4820  have  rather  diffuse  edges.  Wide 
bands  appear  from  A  5020  to  A  5290  and  from  A  5685  to  A  5920.  Diffuse 
bands  are  located  at  A  5310,  A  6810,  and  A  6900.  The  group  in  the  region 
A  6300  appears,  but  the  bands  are  extremely  faint. 


74  A    STUDY   OF   THE    ABSORPTION  SPECTRA. 

At  82°  the  general  absorption  has  increased  in  the  ultra-violet  and  has 
reached  to  about  >l  2800.  It  will  be  noticed  here  that  the  effect  of  rise  in 
temperature  upon  this  general  ultra-violet  absorption  is  greater  for  the 
dilute  solution  than  for  the  concentrated  solution  which  has  been  pre- 
viously described. 

The  band  U  3455  to  3575  at  5°  has  widened  slightly,  having  the  limits 
JU  3445  and  3580  at  82°,  the  widening  being  about  15  Angstrom  units.  This 
band  in  the  concentrated  solution  widened  60  Angstrom  units.  Practically 
no  effect  on  the  bands  from  A  4200  to  A  4900  is  to  be  noticed  with  rise  in 
temperature.  At  the  higher  temperature  the  bands  are  slightly  more  diffuse, 
but  this  change  is  very  small.  The  band  U  5020  to  5290  at  5°  has  widened 
to  >U  5015  and  5285,  about  10  Angstrom  units.  The  corresponding  widen- 
ing for  the  concentrated  solution  was  approximately  50  Angstrom  units; 
although  it  must  be  noted  that  in  the  more  concentrated  solution  this 
widening  was  mostly  due  to  the  increased  absorption  of  the  band  A  5310 
at  the  higher  temperatures.  The  band  I  5685  to  A  5920  at  5°  has  widened 
to  M  5775  and  5930,  about  20  Angstrom  units,  compared  with  a  widening  of 
55  Angstrom  units  for  the  more  concentrated  solutions.  None  of  the  other 
bands  show  any  appreciable  change  with  change  in  temperature. 

A  spectrogram  (Plate  39,  A)  was  made  showing  the  effect  of  tempera- 
ture on  the  absorption  spectrum  of  a  1.66  normal  aqueous  solution  of 
neodymium  bromide,  the  depth  of  layer  being  6  mm.  An  exposure  of  4 
minutes  was  made  to  the  Nernst  glower  (0.8  ampere  and  a  slit-width  of  0.20 
mm.).  The  length  of  exposure  to  the  spark  was  6  minutes.  The  tempera- 
tures, starting  with  the  strip  adjacent  to  the  comparison  spectrum,  were  4°, 
20°,  36°,  50°,  68°,  and  83°. 

At  4°  there  is  complete  absorption  in  the  ultra-violet  up  to  A  2600. 
A  broad  absorption  band  appears  at  A  2660  to  X  2800  and  from  A  2950  to 
A  3060.  These  absorption  bands  appear  with  a  more  or  less  general  absorp- 
tion. Bands  appear  at  /U  3460,  3500,  and  3540.  The  band  at  A  4274  is  weak. 
Weak  and  diffuse  bands  occur  at  U  4440,  4630,  4695,  4825,  5095,  5260, 
6810,  and  6900.  Wider  bands  are  located  at  U  5116  to  5140,  U  5200  to 
5240,  and  >U  5710  to  5850. 

At  83°  the  spectrum  is  almost  exactly  the  same  as  at  4°.  The  ultra- 
violet absorption  is  complete  up  to  >l  3050.  The  bands  at  A  3500  have 
increased  in  width  slightly  and  the  band  A  4274  is  slightly  broader.  The 
bands  that  have  widened  appreciably  are  U  5195  to  5260  and  U  5700  to 
5880.  The  change  in  the  absorption  is  greater  when  the  temperature  is 
changed  from  68°  to  83°.  Up  to  68°  there  is  practically  no  change  in  the 
absorption  spectrum  at  all. 

A  spectrogram  (Plate  39,  B)  showing  the  effect  of  temperature  was 
made,  using  a  0.055  normal  aqueous  solution  of  neodymium  bromide,  the 
depth  of  layer  being  197.4  mm.  This  spectrogram  was  made  for  comparison 
with  that  for  a  1.66  normal  solution  of  the  same  salt  6  mm.  deep.  The 
exposures  to  the  Nernst  glower  lasted  90  seconds  in  this  case  (current  0.8 
ampere  and  slit-width  0.20  mm.).  The  length  of  exposure  to  the  spark  was 
6  minutes.  Starting  with  the  strip  nearest  to  the  comparison  scale,  the 
temperatures  of  the  solution  were  5°,  16°,  29°,  42°,  55°,  68°,  and  84°. 


NEODYMIUM   SALTS.  75 

At  5°  there  is  practically  complete  transmission  of  light  between 
A  3400  and  A  2600,  no  ultra-violet  bands  appearing,  as  was  the  case  for  the 
more  concentrated  solution.  The  bands  AA  4445,  4693,  4760,  4825,  and  5095 
were  somewhat  sharper  than  they  were  in  the  concentrated  solutions. 
The  two  largest  bands  extended  from  A  5200  to  X  5250  and  from  A  5710  to 
A  5850.  As  in  the  case  of  the  more  concentrated  solution,  so  here,  the  greatest 
change  in  the  absorption  took  place  in  the  change  from  68°  to  84°.  The 
ultra-violet  absorption  increased  up  to  X  2900.  The  bands  at  A  3500  became 
considerably  stronger,  but  they  widened  very  little.  The  bands  U  4445, 
4693,  4760,  and  4825  are  somewhat  weaker  than  at  5°.  The  wide  bands 
remained  practically  as  wide  as  at  5°,  X  5200  to  A  5250  and  X  5705  to  5870. 
This  indicates  a  widening  of  about  25  Angstrom  units  for  the  latter  band. 
For  the  more  concentrated  solution  the  widening  of  these  two  bands  was 
25  and  40  Angstrom  units,  respectively.  It  is  thus  seen  that  in  the  more 
concentrated  solutions  the  bands  widen  more  with  rise  in  temperature  than 
they  do  in  the  less  concentrated  solutions.  At  42°  in  the  dilute  solution  there 
appears  a  narrow  band  at  A  6710.  This  increases  in  intensity  with  rise  in 
temperature.  This  band  does  not  appear  at  all  in  the  concentrated  solution. 

A  spectrogram  (Plate  40,  .A)  was  made  of  neodymium  chloride  and 
calcium  chloride  in  water.  Exposures  were  made  for  30  seconds  to  the 
Nernst  glower,  the  current  being  0.8  ampere  and  the  slit-width  0.20  mm. 
The  length  of  exposure  to  the  spark  was  4  minutes.  Starting  with  the 
strip  nearest  the  numbered  scale,  the  temperatures  were  6°,  17°,  31°,  49°, 
63°,  74°,  and  82°. 

The  general  effect  of  the  addition  of  calcium  chloride  is  to  make  all 
the  bands  hazier,  and  to  increase  the  transmission  throughout  the  region 
of  the  band.  At  6°  there  is  a  slight  transmission  throughout  the  ultra- 
violet portion  of  the  spectrum.  As  the  temperature  is  raised  this  general 
transmission  is  decreased,  and  at  82°  practically  no  light  of  shorter  wave- 
length than  A  2800  passes  through  the  solution.  Sharp  bands  occur  at 
A  3464,  A  3500,  A  3535,  A  4276  and  weak  diffuse  bands  at  A  4295,  A  4305, 
A  4340,  A  4445,  A  4620,  A  4695,  A  4760,  A  4825,  A  5095,  A  5130,  A  5225,  A  5260, 
A  5320,  A  5710  to  A  5860,  A  6245,  A  6810,  and  A  6900. 

At  82°  the  bands  in  the  A  3500  region  are  slightly  more  intense  than 
at  6°.  Practically  all  the  bands  from  A  4200  to  A  5200  have  become  much 
weaker  at  the  higher  temperature.  This  is  especially  true  of  the  band  A  4276, 
its  intensity  being  less  than  half  what  it  is  at  6°.  Most  of  the  bands  are 
shifted  to  the  red  with  reference  to  the  same  bands  at  6°.  For  instance, 
A  5095  is  shifted  5  Angstrom  units  towards  the  red.  The  bands  A  4695, 
A  4760,  and  A  4825  are  all  shifted  to  the  red  at  the  higher  temperature, 
and  especially  A  4825,  the  shift  in  this  case  amounting  to  5  Angstrom  units. 
In  the  case  of  these  bands  the  shift  is  not  an  apparent  one  due  to  unsym- 
metrical  broadening,  for  in  this  instance  there  is  no  broadening  at  all. 

The  band  from  A  5710  to  A  5860  at  6°  has  widened  very  unsymmetri- 
cally  and  has  the  limits  A  5710  to  A  5920.  The  short  wave-length  side  is  quite 
sharp  and  its  position  is  practically  independent  of  the  temperature.  The 
long  wave-length  edge  is  quite  broad  and  recedes  quite  rapidly  towards 
the  red  as  the  temperature  is  raised.  The  bands  in  the  red,  AA  6810  and 


76  A    STUDY    OP   THE   ABSORPTION  SPECTRA. 

6900,  grow  fainter  and  fainter  with  rise  in  temperature,  and  have  practically 
disappeared  at  82°.  The  band  X  6245  is  very  weak  at  6°  and  has  disap- 
peared at  about  60°. 

It  will  thus  be  seen  that  not  only  does  the  presence  of  calcium  chloride 
modify  greatly  the  absorption  of  neodymium  chloride,  but  that  it  changes 
the  effects  due  to  temperature  very  fundamentally.  In  pure  neodymium 
chloride  practically  no  bands  decrease  in  intensity  with  rise  in  temperature, 
and  at  present  no  shift  has  been  detected.  When  calcium  chloride  is  added 
to  the  solution  most  of  the  bands  decrease  in  intensity  with  rise  in  tempera- 
ture and  several  are  shifted  towards  the  red  at  the  same  time.  Several 
bands  disappear.  Moreover,  although  the  band  XX  6800  to  6900  widens, 
this  widening  is  entirely  on  the  red  side,  whereas  for  the  pure  neodymium 
chloride  solution  this  widening  always  takes  place  on  both  sides  of  the  band. 

A  spectrogram  (Plate  40,  B)  was  made  to  show  the  effect  of  change 
in  temperature  on  a  2.15  normal  aqueous  solution  of  neodymium  nitrate. 
The  length  of  layer  was  3  mm.  The  exposures  were  for  40  seconds  to  the 
Nernst  glower  (current  0.8  ampere,  slit-width  0.20  mm.).  The  length  of 
exposure  to  the  spark  was  6  minutes.  Starting  with  the  strip  nearest  the 
comparison  spectrum,  the  temperatures  recorded  were  4°,  17°,  29°,  43°,  58°, 
71°,  and  84°. 

The  changes  in  the  spectrum  due  to  this  change  in  temperature  of 
80°  were  very  slight.  The  NO3  band  extends  to  about  X  3250  at  4°,  and  to 
about  X  3280  at  84°.  The  bands  at  X  3500  became  considerably  wider  and 
their  edges  more  diffuse  at  the  higher  temperatures.  At  the  lower  tem- 
peratures fine  bands  appear  at  XX  5210,  5225,  and  5240.  At  84°  these  bands 
all  merge  into  a  single  band.  The  red  band  extends  from  X  5705  to  X  5860 
at  4°.  The  band  at  X  5820  is  very  faint  at  the  lower  temperatures.  At  84° 
it  is  unrecognizable.  At  this  temperature  the  red  band  extends  from  X  5700 
to  ^5880.  The  widening  of  this  band  for  the  concentrated  solution  is 
somewhat  greater  than  for  the  dilute  solution,  but  the  effect  of  concentra- 
tion is  very  slight.  This  is  to  be  expected  since  the  effect  of  temperature 
itself  is  so  very  minute. 

A  spectrogram  was  made  of  a  1.66  normal  aqueous  solution  of  neodym- 
ium bromide  54.6  mm.  deep.  The  exposures  were  3  minutes  to  the  Nernst 
glower  and  6  minutes  to  the  spark.  The  current  in  the  Nernst  glower  was 
0.8  ampere  and  the  slit-width  0.20  mm.  Starting  with  the  strip  nearest  the 
comparison  scale,  the  temperatures  were  6°,  20°,  33°,  47°,  62°,  73°,  and  82°. 

The  effect  of  rise  in  temperature  on  the  absorption  spectra  of  this 
salt  was  quite  marked,  practically  all  of  the  bands  broadening  and  becom- 
ing more  intense.  At  6°  the  ultra-violet  absorption  extended  to  X  3600. 
At  82°  it  had  advanced  to  X  3800.  Very  narrow  and  fine  bands  appear  at 
XX  4186, 4300, 4308, 4345,  6240,  6265,  6290,  6305,  and  much  broader  bands  at 
^6380  and  X  6740.  Wide  bands  occur  from  ^4390  to  4480,  ,1*4550  to 
4850,  XX  4990  to  5340,  XX  5650  to  5950,  and  XX  6760  to  6930,  at  6°.  At  82° 
these  bands  have  the  following  limits,  respectively:  XX  4380  to  4500,  XX  4540 
to  4910,  XX  4960  to  5370,  XX  5620  to  5990,  and  XX  6730  to  6960. 

A  spectrogram  (Plate  38,  B)  was  made  of  a  2.96  normal  aqueous 
solution  of  neodymium  nitrate  38.5  cm.  deep.  An  exposure  of  3  minutes 


NEODYMIUM    SALTS.  77 

was  made  to  the  Nernst  glower,  the  current  being  0.8  ampere  and  the  slit- 
width  0.20  mm.  The  length  of  exposure  to  the  spark  was  6  minutes. 
Starting  with  the  strip  nearest  the  comparison  scale  the  temperatures 
were  7°,  17°,  30°,  44°,  59°,  70°,  and  82°. 

At  7°  there  is  practically  complete  absorption  in  the  ultra-violet  up 
to  A  4600,  due  to  the  absorption  of  the  NO3  group.  The  edge  of  the  band 
is  very  sharp.  Other  bands  are  as  follows:  A  4270  to  A  4288,  A  4386  to 
A  4500,  A  4538  to  A  4870,  A  4970  to  A  5370,  X  5620  to  A  6005,  A  6240  to  A  6270, 
and  A  6705  to  A  6970. 

It  should  be  noticed  here  that  the  absorption  spectrum  of  neodymium 
nitrate  under  the  present  conditions  is  quite  different  from  the  absorption 
of  a  similar  solution  of  neodymium  chloride.  In  the  case  of  the  chloride 
there  was  a  very  great  amount  of  absorption  throughout  the  ultra-violet 
and  violet  portions  of  the  spectrum.  In  the  case  of  the  nitrate  there  is 
almost  complete  absorption  up  to  X  3600  and  from  that  wave-length  to 
A  4270  there  is  complete  transmission.  In  this  region  appeared  several 
narrow  and  sharp  bands  in  the  neodymium  chloride  absorption  spectrum. 

From  the  spectrum  shown  in  the  upper  strip  and  for  which  the  tempera- 
ture was  82°  we  see  that  the  NO3  band  extends  to  A  3615.  The  band  A  4274 
has  become  about  5  Angstrom  units  wider  than  it  was  at  7°.  A  wide  and 
weak  band  appears  at  A  4350,  and  this  is  considerably  stronger  than  at  the 
lower  temperatures.  The  positions  of  the  other  bands  are:  A  4380  to 
A  4560,  A  4535  to  A  4870,  A  4970  to  A  5390,  A  5615  to  A  6025,  and  A  6700  to 
A  6970.  The  increase  in  width  of  these  bands  due  to  raising  the  temper- 
ature from  7°  to  82°,  is  60,  20,  25,  and  about  0  Angstrom  units,  respectively. 

A  spectrogram  was  made  of  the  absorption  spectra  of  a  2.15  normal 
solution  of  neodymium  nitrate  3  mm.  deep.  Starting  with  the  strip  nearest 
the  numbered  scale,  the  temperatures  were  4°,  17°,  29°,  44°,  58°,  71°,  and  84°. 

As  the  temperature  rises  the  NOS  band  widens  slightly.  The  bands 
in  the  region  of  A  3500  become  more  diffuse  and  slightly  wider.  The  same 
is  true  of  the  bands  at  A  5200.  The  broad  band  at  A  5800  widens,  especially 
on  the  long  wave-length  edge. 

A  spectrogram  (Plate  40,  B)  was  made  of  a  very  dilute  solution  of 
neodymium  nitrate  in  aqueous  solution  of  0.036  normal  concentration  and 
197  mm.  depth  of  cell.  The  length  of  exposure  to  the  Nernst  glower  was 
20  seconds,  current  being  0.8  and  slit-width  0.20  mm.  The  length  of  ex- 
posure to  the  spark  was  5  minutes.  Starting  with  the  strip  nearest  the  com- 
parison spark-spectrum,  the  temperatures  were  9°,  22°,  42°,  56°,  69°,  and  78°. 

The  effect  of  temperature  on  the  absorption  of  neodymium  at  this 
concentration  is  very  slight.  At  9°  there  is  almost  complete  absorption 
up  to  A  3300,  due  to  the  N03  band.  Bands  are  located  at  A  3460,  A  3500, 
A  3530,  A  4273  (weak),  A  4445,  A  4610,  A  4692,  A  4756,  A  4820,  A  5093,  A  5136, 
A  5197  to  A  5247,  A  5255,  A  5330,  A  5705  to  A  5860,  A  6800  and  A  6900. 

At  78°  the  NO3  has  advanced  about  30  Angstrom  units  towards  the 
red.  The  bands  in  the  region  of  A  3500  have  widened  slightly.  The  inten- 
sities of  the  other  bands  have  changed  but  little.  The  wide  band  in  the 
red  extends  from  A  5705  to  A  5875,  there  being  a  slight  widening  on  the  long 
wave-length  edge  of  the  band.  The  bands  A  6800  and  A  6900  are  slightly 


78  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

more  diffuse  than  at  9°,  but  this  change  is  very  small.  The  bands  from 
>l  4200  to  >l  5000  seem  to  be  slightly  shifted  towards  the  red  at  the  higher 
temperatures.  In  all,  this  shift,  however,  is  not  greater  than  2  or  3  Ang- 
strom units. 

NEODYMIUM  SALTS  IN  GLYCEROL. 

A  run  was  made  to  test  whether  Beer's  law  holds  for  glycerol  solutions. 
Plate  35,  A,  represents  a  spectrogram  ranging  from  0.84  to  0.105  normal, 
the  amount  of  absorbing  matter  being  kept  constant.  The  more  dilute 
solutions  show  greater  general  absorption  in  the  ultra-violet.  Otherwise 
Beer's  law  is  found  to  hold. 

Plate  43,  A,  is  the  spectrogram  of  a  solution  of  neodymium  chloride 
in  glycerol  taken  in  the  silica  cell  at  various  temperatures.  The  plate 
shows  a  slight  widening  of  the  bands,  but  this  is  very  small.  Some  of  the 
finer  bands  indicate  a  slight  shift  towards  the  red  with  rise  in  temperature. 
This,  however,  is  quite  small  and  never  amounts  to  more  than  3  or  4 
Angstrom  units  for  any  band. 

Plate  46,  A,  shows  the  effect  of  rise  in  temperature  of  solutions  contain- 
ing neodymium  and  aluminium  or  calcium  chlorides  in  glycerol.  In  the 
third  and  fourth  strips  it  is  to  be  noticed  that  the  wide  band  at  X  5800  is 
shifted  slightly  to  the  red.  The  band  at  about  A  4295  seems  to  be  shifted 
2  or  3  Angstrom  units  to  the  red.  The  shift  is  very  small  and  is  obscured 
in  part  by  the  increased  diffuseness  of  the  bands  at  the  higher  temperature. 

Plate  29,  B,  represents  the  effect  of  rise  in  temperature  on  the  absorp- 
tion spectra  of  pure  neodymium  chloride  in  glycerol.  The  shift  of  the  bands 
in  this  case  can  hardly  be  noticed.  The  effect  of  the  presence  of  calcium 
is  to  cause  the  temperature  shift  of  the  bands  to  be  increased.  The  effect 
is  not  as  great  as  it  is  in  aqueous  solutions. 

The  absorption  spectrum  of  neodymium  chloride  (Plate  34,  A  and  B) 
in  glycerol  is  very  similar  to  that  of  an  aqueous  solution.  The  ultra-violet 
bands  M  3475  and  3550  are  quite  strong  and  sharp.  A  weak  band  appears  at 
A  3520.  For  the  3  mm.  depth  of  cell  and  smallest  concentration  the  follow- 
ing bands  appear:  U  4290  (weak),  4710  (very  weak),  5120  (wide,  hazy,  and 
apparently  a  triplet),  5230,  5240  (strong  and  fairly  sharp),  5250,  5270  (weak 
and  fuzzy),  5740  (wide  and  hazy),  5790,  5805,  5820,  and  5850.  The  latter 
three  bands  practically  merge  into  a  single  band,  the  transmission  between 
them  being  very  weak. 

The  greatest  concentration  and  the  9  mm.  depth  of  cell  (upper  strip 
of  Plate  34,  A)  shows  several  additional  bands:  /U  3600,  4190  (very  diffuse), 
4288,  and  two  very  fine  components  at  4270  and  4305,  4330,  4345,  4365,  a 
wide  (50  Angstrom  units)  band  at  4460,  and  similar  but  weaker  bands  at 
4620,  4840,  5340,  5940,  6240,  6265,  6400,  6800,  with  narrower  and  sharper 
bands  at  4710,  4730,  4760,  4790,  5170,  and  5190. 

The  "glycerol  "  bands  are  very  similar  to  the  "water  "  bands  but  are 
all  of  slightly  greater  wave-length.  The  sharp  "water  "  band  at  ^  4274  is 
composed  of  three  bands  in  the  glycerol  solution.  The  "glycerol "  bands 
are  quite  persistent  and  for  a  solution  containing  10  per  cent  water  the 
bands  are  practically  "glycerol"  bands.  In  general,  the  "water"  and 
"  glycerol "  bands  are  so  close  to  one  another  that  we  can  not  tell  whether 


NEODYMIUM   SALTS.  79 

both  bands  coexist  when  the  neodymium  salt  is  dissolved  in  a  mixture  of 
the  solvents.  But  the  A  4288  band  apparently  shifts  gradually  into  the 
A  4274  "  water  "  band.  No  sign  of  the  two  bands  coexisting  is  to  be  seen. 

NEODYMIUM  NITRATE  IN  NITRIC  ACID. 

Plate  42,  B,  gives  the  absorption  spectra  of  neodymium  nitrate  in 
nitric  acid.  The  effect  of  free  nitric  acid  is  very  pronounced.  All  the  bands 
are  wide  and  diffuse  and  differ  very  much  from  the  absorption  when  there 
is  no  free  acid.  The  first  band  to  appear  is  A  5830  and  it  appears  as  a  very 
faint  diffuse  band.  Then  come  the  bands  AA  3470,  3520,  3550,  5130,  5250, 
5730,  5970,  and  for  a  greater  depth  of  cell  AA  4280,  4310,  4340,  4360,  4390  to 
4460,  4480,  4600,  4650  (weak),  4705  (strong),  4745  (strong),  4840,  5385 
(strong),  6245,  6275,  and  6770. 

In  general,  it  has  been  shown  that  the  presence  of  nitric  acid  is  to  shift 
the  uranyl  and  uranous  bands  to  the  violet.  This  does  not  seem  to  be  the 
effect  of  adding  a  large  amount  of  acid  to  neodymium  nitrate  in  aqueous 
solution.  Many  of  the  above  bands  do  not  seem  to  be  bodily  shifted  to  the 
red,  but,  like  the  band  marked  A  4280,  they  are  widened  on  the  red  side. 
The  narrow  band  A  4274  of  the  neutral  nitrate  lies  within  the  broad  and 
diffuse  band  A  4280.  As  will  be  remembered,  the  action  of  free  nitric  acid 
on  the  uranyl  nitrate  bands  was  to  cause  them  to  become  sharper.  At  the 
same  time  the  bands  were  shifted  to  the  violet. 

Some  of  the  bands  that  Stahl  considered  as  absent  in  the  presence  of 
nitric  acid  appear  on  our  plates,  the  band  A  4705  above  apparently  being  his 
bands  AA  4690  and  4710. 

SPECTROPHOTOQRAPHY   OF   CHEMICAL   REACTIONS. 

During  the  progress  of  the  work  quite  a  number  of  photographs  were 
made  of  a  salt  in  mixtures  of  two  solvents.  It  seemed  of  interest  to 
photograph  the  absorption  spectra  of  a  salt  when  different  amounts  of 
an  acid  were  added  to  the  given  salt  in  solution.  In  the  case  of  uranyl 
salts  several  were  found  to  have  different  absorption  spectra.  In  the  case  of 
neodymium,  however,  it  was  found  that  the  various  salts  had  practically 
the  same  absorption  spectra.  The  absorption  of  the  acetate  was,  however, 
found  to  differ  from  that  of  the  other  salts,  so  that  the  chemical  changes 
produced  by  adding  various  acids  were  photographed  with  the  aid  of  the 
spectroscope. 

Plate  41,  B,  represents  the  absorption  spectra  of  an  aqueous  solution 
of  neodymium  acetate,  the  concentration  being  kept  constant  and  only 
the  depth  of  cell  being  changed. 

It  will  be  seen  from  a  mere  glance  that  the  absorption  spectra  of  the 
acetate  is  quite  different  from  that  of  the  other  neodymium  salts.  All  the 
bands  are  much  wider  and  less  intense.  Many  of  the  broad  bands  that 
appear  as  several  finer  bands  in  the  spectra  of  the  other  salts,  appear  here 
as  single  and  very  weak  when  the  depth  of  cell  is  small. 

The  following  are  the  wave-lengths  of  a  few  of  the  bands:  AA  3485, 
3520,  3820,  4040,  4200,  4295,  4333,  4360,  4460,  4630,  4720,  4770,  4850,  5140 
(very  wide  and  weak),  5260,  5360,  5660,  5800  to  5860,  6820,  and  6950. 


80 


A    STUDY   OF   THE   ABSORPTION   SPECTRA. 


It  will  be  noticed  that  all  the  bands  are  10  to  20  Angstrom  units  farther 
to  the  red  than  the  corresponding  bands  of  the  other  neodymium  salts. 

The  A  section  of  Plate  41  represents  the  effect  of  adding  nitric  acid  to 
a  solution  of  neodymium  acetate.  The  first  strip  of  A  contains  nitric  acid 
and  shows  that  the  acetate  bands  have  been  shifted  some  10  Angstrom 
units  towards  the  violet  by  this  addition  of  acid.  This  shift  occurs  before 
any  other  change  of  the  acetate  bands  takes  place. 

Plate  41,  A,  represents  a  spectrophotograph  of  the  effect  of  adding 
nitric  acid  to  an  aqueous  solution  of  neodymium  acetate.  The  addition 
of  nitric  acid  causes  the  absorption  in  the  ultra-violet  to  increase.  The 
general  effect  on  the  neodymium  bands  is  to  cause  the  bands  to  become 
sharper,  and,  then,  as  more  and  more  acid  is  added,  to  make  the  bands 
diffuse  again.  When  the  bands  are  sharpest  they  are  practically  the  same 
as  the  bands  of  neodymium  nitrate  in  water.  It  requires  the  addition  of 
a  very  considerable  amount  of  nitric  acid  to  produce  the  nitrate  neodymium 
bands.  A  description  of  the  plate  is  to  be  found  on  page  150. 

The  group  of  bands  in  the  region  ^  3500  in  the  first  and  seventh  strips 
appear  to  be  slightly  displaced  to  the  red.  In  fact,  all  the  "  nitrate  "  bands 
of  the  third  and  fourth  strips  are  some  10  Angstrom  units  farther  towards 
the  violet  than  the  bands  of  the  first  and  seventh  strips. 


Strip  1. 

Strip  3. 

Strip  7. 

3470 

3465 

3470 

3510  very  fuzzy 
3550 

3505 
3533  sharp 

3515  very  fuzzy 
3550 

4285 

3553 

4285 

4705 

4275 

4705 

4695 

In  strip  1  there  is  a  strong  band  at  >l  5230  to  >l  5250.  In  strip  2  appears 
a  very  fine  and  weak  band  on  the  shorter  wave-length  side  of  the  wide  band 
at  X  5240.  In  strips  3  and  4  the  two  bands  are  of  equal  intensity  and  are 
located  at  ^  5225  and  /I  5234.  In  strip  5  a  band  appears  on  the  red  side  of 
A  5234.  At  the  same  time  ^  5234  has  become  very  much  stronger  than 
A  5225.  In  strip  7  ^  5225  has  become  very  weak.  In  strip  7  there  are  weak 
and  fine  bands  at  X  5205,  5225  and  a  band  from  ^  5230  to  ^  5250. 

The  group  of  bands  at  A  5800  behave  in  the  same  way.  In  strip  4 
there  are  bands  at  JU  5730,  5755,  5775,  5800,  and  5820.  In  strip  1  is  a  hazy 
band  at  A  5750  and  others  at  U  5790,  5820,  and  5870.  In  strip  7  there  are 
four  bands,  two  at  X  5730  to  5760  and  two  at  yl  5770  to  5830.  The  bands 
U  6800,  7040,  and  7100  appear  only  in  the  central  strips. 

A  spectrogram  was  made  to  show  the  coexistence  of  the  "  water  "  and 
"  alcohol  "  bands  of  neodymium  chloride.  The  spectrogram  is  shown  as 
Plate  43,  A.  Anhydrous  neodymium  chloride  was  dissolved  in  a  solution 
containing  8  per  cent  water  and  92  per  cent  ethyl  alcohol.  The  first  four 
strips  represent  a  Beer's  law  run,  the  concentrations  being  0.5,  0.3,  0.1,  and 
0.05  normal,  the  most  concentrated  solution  being  the  one  whose  spectrum 
is  next  to  the  scale.  The  last  three  strips  represent  a  constant  concentra- 
tion where  the  depth  of  cell  is  increased. 


NEODYMIUM    SALTS. 


81 


The  spectrogram  shows  that  Beer's  law  does  not  hold,  the  more  con- 
centrated solutions  being  the  greater  absorbers.  This  is  especially  true  of 
the  alcoholic  portion  of  the  absorption.  In  strip  1  the  "  alcoholic  "  band 
corresponding  to  the  "  water  "  band  ^  4274  has  about  the  same  intensity 
as  the  "  water  "  band.  In  strip  4,  however,  the  "  alcohol "  band  has  become 
very  weak,  indeed,  while  the  water-band  has  slightly  increased  in  absolute 
intensity  as  compared  with  strip  1.  Several  other  bands  indicate  the  same 
change.  The  "  alcohol  "  bands  thus  weaken  in  intensity  as  the  concen- 
tration is  decreased,  while  the  "  water  "  bands  do  not. 

In  this  connection  experiments  are  now  in  progress  in  which  it  will  be 
tested  whether  changes  in  temperature,  the  addition  of  chemical  reagents, 
etc.,  affect  the  different  bands  in  the  same  way. 

Plate  43,  B,  represents  the  effect  of  adding  hydrobromic  acid  to  an 
aqueous  solution  of  neodymium  acetate.  The  first  strip  represents  the 
absorption  of  a  solution  of  neodymium  acetate  in  water  to  which  about  a 
drop  of  hydrobromic  acid  has  been  added.  Strip  2  represents  the  same  to 
which  several  more  drops  of  hydrobromic  acid  have  been  added.  The 
remaining  strips  represent  the  absorption  of  the  same  solution  to  which 
more  and  more  hydrobromic  has  been  added. 

The  first  strip  gives  the  characteristic  acetate  spectrum.  In  order  to 
give  the  effect  of  the  acid  the  wave-lengths  of  the  bands  of  the  acetate  meas- 
ured on  the  film  itself  are  given  and  compared  with  the  spectrum  of  strip  2. 


Strip  1. 

Strip  2. 

Strip  1. 

Strip  2. 

.... 

3465 
3510 
3543 

4800  to  5150 
gen.  absorp. 

{  4830 
\  5105 
[  5140 

4290 

3560 
4285 

5240 

/  5225 
I  5240 

4450 

f  44451 
\  4460  f 

5745 
5760 

5740 
5760 

4715 

4705 

- 

5775 

4775 

4775 

5790 

.... 

5825 

5810 

5870 

The  effect  of  adding  a  very  small  amount  of  hydrobromic  acid  is  very 
pronounced.  The  addition  of  larger  amounts  of  hydrobromic  acid  has 
very  little  effect.  The  shifting  effect  of  hydrobromic  acid  is  very  small  as 
compared  with  the  same  effect  produced  by  nitric  acid  on  the  nitrate.  The 
presence  of  a  large  amount  of  hydrobromic  acid  does  not  make  the  bands 
hazy  and  wide. 

Plate  44,  A,  represents  the  effect  of  adding  hydrochloric  acid  to  an 
aqueous  solution  of  neodymium  acetate.  The  first  strip  represents  the 
absorption  of  the  pure  aqueous  solution  of  the  acetate.  The  second  strip 
represents  the  absorption  of  the  same  to  which  one  drop  of  hydrochloric 
acid  has  been  added.  The  third  strip  represents  the  absorption  of  the 
solution  to  which  two  more  drops  of  acid  have  been  added.  The  acid  used 
was  concentrated.  The  following  table  represents  in  part  the  changes 
which  the  addition  of  acid  has  caused  to  take  place. 


82 


A    STUDY    OF   THE    ABSORPTION   SPECTRA. 


It  will  be  seen  that  the  addition  of  but  a  small  amount  of  acid  caused 
the  appearance  of  a  large  number  of  fine  bands,  especially  in  the  region 
of  H  5800.  It  also  caused  a  very  considerable  shift  of  all  the  bands  to  the 
violet,  an  action  similar  to  that  of  nitric  acid.  Further  addition  of  acid 
brought  out  a  spectrum  very  similar  to  that  of  neodymium  chloride  as 
shown  by  strips  3  and  4.  Still  further  addition  of  acid  produces  other 
changes,  one  being  the  appearance  of  new  bands  in  the  region  /I  5900. 

Plate  45,  A,  gives  a  spectrogram  where  known  amounts  of  hydro- 
chloric acid  were  added  to  an  aqueous  solution  of  neodymium  acetate. 


Strip  1. 

Strip  2. 

Strip  3. 

Strip  6. 

3485 

3465 

3465(s) 

3530 
3560 

3510 
3540 

3510 
3540s 

The  whole  group 
is  very  weak 

.... 

3560 

3560 

and  diffuse 





3580 

4297 

4285 

4285 

!4285  very  weak 
5305  very  weak 
5350  very  weak 

47101 
4775  \ 
4845  J 

4710  } 
4775  [ 
4845  J 

5140 

r  5110 
I  5140 

.... 

5260 

f  5225  ] 
\  5245  [ 
[  5235  j 

5230s 
5245s 

5230  very  weak 
5245  very  weak 

5760 

5740 

5740 

5750 

5810 

5760 

5760 

5785 

5850 

5780 

5780 

5795 

5810 

5815 

5815 

5900 

5830 

5930 

5865 

5870 

5895 

5910 

A  spectrogram  (Plate  44,  J5)  was  made  of  mixtures  in  various  propor- 
tions of  neodymium  acetate  and  neodymium  chloride  in  water.  Strip 
1  is  the  pure  acetate  and  strip  7  the  pure  chloride.  The  intermediate  strip 
represents  mixtures,  the  amount  of  chloride  increasing  from  the  bottom  up- 
wards. The  concentration  of  neodymium  was  kept  constant. 

From  this  spectrogram  evidence  is  obtained  that  each  of  the  two  salts 
has  its  own  spectrum.  As  the  amount  of  acetate  is  decreased  the  acetate 
bands  gradually  decrease  in  intensity  and  finally  disappear.  At  the  same 
time  the  chloride  bands  increase  in  intensity. 

The  band  ^  5225  apparently  is  a  chloride  band,  and  does  not  appear 
in  the  acetate  solution.  On  the  other  hand,  the  band  A  5830  and  the  very 
diffuse  band  A  5860  appear  to  be  acetate  bands,  and  gradually  disappear 
as  the  amount  of  acetate  decreases. 


NEODYMIUM    SALTS.  83 

A  question  which  was  raised  by  a  study  of  some  of  the  other  spectro- 
grams was  whether  by  the  addition  of  hydrochloric  acid  to  the  acetate 
different  chemical  compounds  were  formed.  In  the  above  spectrogram  only 
two  sets  of  bands  appear,  and  it  thus  seems  very  probable  that  when  hydro- 
chloric acid  is  added  to  the  acetate  more  than  two  compounds  exist,  for 
there  are  more  than  two  sets  of  bands.  Indeed,  it  seems  probable  that 
there  is  a  whole  series  of  compounds  or  systems  formed  between  the  acetate  on 
the  one  hand  and  the  chloride  on  the  other. 

Plate  45,  B,  represents  the  effect  of  adding  hydrochloric  acid  to  an 
aqueous  solution  of  neodymium  citrate.  The  absorption  spectrum  of  the 
citrate  is  very  similar  to  that  of  the  acetate,  and  the  changes  in  the  absorp- 
tion spectra  are  very  similar  to  those  that  take  place  when  mixtures  of  the 
acetate  and  chloride  are  dissolved  in  water.  In  other  words,  there  are 
bands  here:  "  citrate  "  bands  which  are  very  similar  to  the  "  acetate  "  bands. 
As  hydrochloric  acid  is  added  the  characteristic  "  citrate  "  bands  gradually 
decrease  in  intensity  while  the  "chloride"  bands  increase  in  intensity. 
There  is  no  evidence  here  of  more  than  two  chemical  compounds. 


SUMMARY. 

No  salts  show  the  complexity  of  absorption  spectra  better  than  those 
of  neodymium  and  erbium.  Some  of  the  bands  are  wide  and  diffuse,  some 
narrow  and  strong — in  fact  bands  of  very  great  diversity  of  appearance  are 
present.  In  any  given  solvent  the  absorption  spectra  of  the  various  salts 
are  very  similar  and  in  many  cases  practically  identical.  But  when  the 
solutions  are  very  concentrated  or  when  the  salts  themselves  are  investi- 
gated, it  is  found  that  the  absorption  spectra  are  entirely  different  for  each 
salt.  The  fact  that  the  absorption  of  different  salts  in  the  same  solvent  is 
very  similar  is  a  strong  argument  that  the  solvent  plays  a  very  important 
rdle  in  the  absorption  of  light.  This  view  is  very  much  strengthened  when 
it  is  found  that  the  absorption  in  different  solvents  is  different,  and  that  in 
mixtures  of  solvents  both  solvent  bands  coexist. 

During  the  work  on  the  absorption  of  uranyl  nitrate  to  which  sulphuric 
acid  was  added,  the  very  fine  banded  absorption  spectra  of  nitric  oxide 
were  obtained.  From  the  conditions  of  the  experiment  it  seems  very  prob- 
able that  this  nitric  oxide  was  in  solution.  Granting  that  this  is  the  case, 
the  experiment  shows  that  the  solvent  itself  under  some  conditions  may 
not  have  any  effect  upon  the  absorption  spectra.  It  seems  reasonable  to 
suppose  that  it  is  when  chemical  combination  between  solvent  and  solute 
takes  place  that  the  absorption  of  light  is  greatly  modified. 

In  the  case  of  neodymium  bands  it  is  very  difficult  to  change  the 
wave-length  of  the  bands.  Becquerel  and  others  show  that  there  are  small 
changes  as  the  neodymium  is  cooled  to  very  low  temperatures.  The  ab- 
sorption spectra  of  salts  at  600°  indicate  but  slight  changes  in  wave-length 
compared  with  the  salts  at  0°.  For  some  bands  the  shift  is  about  10  Ang- 
strom units.  Our  work  shows  practically  no  shift  in  the  absorption  bands 
of  pure  aqueous  solutions  between  0°  and  90°  C.  However,  when  calcium 
or  aluminium  is  present,  in  some  cases  there  are  shifts. 


84  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

The  absorption  spectra  of  neodymium  chloride  have  been  photographed 
in  glycerol  and  alcohol  solutions.  There  are  indications  of  alcohol-  and 
glycerol-bands.  The  latter  are  more  persistent  than  the  alcohol-bands.  In 
the  case  of  glycerol  there  seemed  to  be  one  band  that  gradually  shifted 
from  the  water  to  the  glycerol  position,  indicating  the  possibility  of  the 
existence  of  intermediate  glycerolates. 

The  effect  of  free  nitric  acid  on  the  bands  of  neodymium  nitrate  is  to 
cause  them  to  become  much  broader  and  more  diffuse  than  the  bands  of 
the  neutral  salt.  Some  of  the  bands  are  caused  to  broaden  more  on  the  red 
than  on  the  violet  side.  The  effect  of  free  nitric  acid  on  the  neodymium 
bands  is  thus  very  different  from  the  effect  on  the  uranyl  nitrate  bands. 

Early  in  the  work  it  was  intended  to  alter  conditions  so  that  each  band 
could  be  followed  throughout  the  various  changes  that  it  underwent.  In 
most  cases,  however,  this  is  at  present  very  difficult  to  do,  on  account  of 
the  very  sudden  changes  in  the  character  of  the  spectra,  and  in  many  cases 
also  on  account  of  the  diffuseness  of  the  bands.  For  instance,  the  band 
A  4274  is  certainly  one  of  the  most  characteristic  bands  of  the  water-spec- 
trum. In  glycerol  it  is  found  that  apparently  this  band  gradually  shifts 
to  A  4288  for  a  pure  glycerol  solution.  For  solutions  containing  a  large 
amount  there  appear  fine  satellites  at  A  4270  and  A  4305.  In  alcohol  the 
band  appears  at  A  4290.  The  band  A  4274  does  not,  however,  shift  into 
the  alcohol-band.  In  a  solution  of  neodymium  nitrate  in  water  as  made 
by  Anderson  there  appear  two  strong  bands  close  together,  the  distance 
between  the  opposite  edges  being  about  10  Angstrom  units,  and  between 
the  adjacent  edges,  2  Angstrom  units.  Neodymium  nitrate  and  sulphate 
crystals  each  give  two  strong  components,  but  in  this  case  the  distance 
between  the  opposite  edges  is  15  Angstrom  units,  and  between  the  adjacent 
edges  6  Angstrom  units.  In  other  words,  in  the  neodymium  nitrate  crys- 
tal the  components  are  farther  apart  than  in  the  nitrate  solution  as  made 
by  Anderson.  In  the  solutions  made  by  Jones  only  one  component 
appears.  A  remarkable  result  manifests  itself  when  the  water  of  crystal- 
lization of  the  sulphate  and  nitrate  crystals  is  driven  off.  The  rather 
paradoxical  effect  is  to  cause  the  "A  4274  "  bands  to  become  weaker  and 
appear  as  a  single  band.  In  the  case  of  neodymium  nitrate,  driving  off  the 
water  of  crystallization  causes  many  of  the  bands  to  be  shifted  towards 
the  red.  For  the  sulphate  the  drying  results  in  a  shift  of  some  bands  to 
the  violet,  while  other  bands  remain  unshifted.  The  dry  nitrate  bands  in 
several  photographs  made  by  Anderson  are  all  of  some  50  Angstrom  units 
greater  wave-length  than  the  dry  chloride,  dry  sulphate,  or  crystal  sulphate 
bands.  It  is  at  present  premature  to  attempt  to  interpret  these  changes, 
since  the  intermediate  steps  have  not  been  followed.  Much  work  remains 
to  be  done  in  this  direction. 

In  aqueous  solutions  it  has  been  found  that  the  absorption  of  neodym- 
ium acetate  is  different  from  that  of  the  chloride,  bromide,  and  nitrate. 
By  adding  inorganic  acids  to  the  acetate,  photographs  have  been  made  of 
the  spectrum,  as  the  acetate  was  changed  to  another  salt.  These  spectra 
indicate  that  in  some  of  the  reactions  there  probably  exist  several  systems  or 
compounds  between  the  acetate  and  the  salt  of  the  acid  added. 


CHAPTER  XI. 

URANIUM  SALTS. 

Absorption  spectra  of  uranium  compounds. — Absorption  spectra  of  uranyl 
chloride. — Absorption  spectra  of  uranyl  nitrate. — Absorption  spectra  of  uranyl 
bromide,  sulphate,  and  acetate. — Spectrophotography  of  the  chemical  reac- 
tions of  uranyl  salts;  conductivity  data. — The  phosphorescent  and  fluorescent 
spectra. — Absorption  spectra  of  uranous  salts. 

THE   ABSORPTION  SPECTRA   OF   URANIUM   COMPOUNDS. 

There  are  quite  a  large  number  of  spectra  of  the  various  compounds 
and  decomposition  products  of  the  element  uranium.  The  absorption 
spectra  consist  chiefly  of  the  banded  spectra  of  the  uranyl  and  uranous 
compounds.  Uranyl  salts  in  solution  are  yellow  and  their  absorption 
spectra  consist  of  a  broad  band  of  general  absorption  in  the  ultra-violet, 
which  extends  more  and  more  into  the  region  of  longer  wave-lengths  as  the 
amount  of  uranyl  salt  solution  in  the  beam  of  light  is  increased.  The  edge 
of  this  absorption  band  as  it  gradually  advances  through  the  violet  and 
into  the  blue  shows  several  diffuse  bands  about  50  Angstrom  units  wide  and 
about  100  Angstrom  units  distant  from  each  other.  These  comparatively 
fine  bands,  about  twelve  in  number,  are  weak,  having  very  diffuse  edges, 
and  can  be  photographed  only  when  they  lie  near  the  edge  of  the  general 
absorption  band.  Among  those  who  have  carried  out  investigations 
upon  the  absorption  spectra  of  these  compounds  may  be  mentioned: 
H.  Oeffinger,1  H.  Becquerel,2  W.  Boehlendorff,3  O.  Knoblauch,4  E.  Deussen,5 
Formanek,8  Hartley,7  Houstoun  and  Russel,8  Jones  and  Strong,9  Strong,10 
and  others. 

In  the  discussion  of  the  uranyl  bands  it  will  be  found  convenient  to 
designate  them  by  the  letters  a,  b,  c,  d,  etc.,  the  band  a  being  of  the  greatest 
wave-length,  and  the  wave-lengths  of  the  other  bands  gradually  decreasing. 
In  general  it  will  be  found  that  this  classification  is  very  useful,  and  upon 
general  observations  it  might  be  supposed  that  each  band  had  its  origin 
in  a  particular  vibration  of  the  vibrating  system.  But  at  low  temperatures 
these  bands  are  found  to  consist  of  a  number  of  much  finer  bands,  and  the 
absorption  spectra  become  very  complicated  indeed,  so  that  it  is  clear 
that  changes  which  are  observed  at  ordinary  temperatures  may  be  due  to 
relative  changes  in  the  groups  of  five  bands  composing  the  larger  bands, 

1  Ueber  die  Lichtabsorption  der  Uransalze,  Inaug.  Diss.,  Tubingen,  1866. 
1  Ann.  Chim.  Phys.,  (6)  14, 170-257  (1888). 
s  Inaug.  Diss.,  Erlangen,  1890. 
« Wied.  Ann.,  43,  738-783  (1891). 
1  Ibid.,  66,  1128-1148  (1898). 

•  Die  qualitative  Spectralanalyse  anorg.  K6rper,  Berlin,  1900. 
i  J.  Chem.  Soc.,  83,  221-246  (1903). 

8  Proc.  Roy.  Soc.  Edinb.,  29,  n,  68. 

•  Phys.  Zeit.,  10,  499  (1909). 

10  Phys.  Rev.,  29,  555  (1909);  30,  279  (1910). 

85 


86 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 


a,  6,  c,  d,  etc.  For  instance,  shifts  in  the  position  of  the  bands,  a,  b,  c,  etc., 
due  to  relative  changes  in  the  intensity  of  the  components,  may  be  observed 
when  the  frequency  of  none  of  the  component  bands  has  been  changed  at  all. 
Becquerel  '  found  that  the  position  and  intensity  of  the  absorption 
bands  of  a  crystal  depend  on  the  direction  in  which  the  light  traversed  the 
crystal.  To  study  this  phenomenon  of  absorption  he  cut  sections  of  crystals 
in  three  different  directions.  One  section  was  cut  parallel  to  the  optic  axes 
that  cut  each  other  obliquely  ("axe  moyen  "),  one  section  perpendicular 
to  the  bisector  of  the  acute  angle  ("  bissectrice  aigue")>  and  another  section 
perpendicular  to  the  bisector  of  the  obtuse  angle  ("  bissectrice  obtuse  "). 
Crystals  of  uranyl  nitrate  belong  to  the  orthorhombic  type.  Becquerel 
measured  the  wave-lengths  of  the  three  bands,  a,  b,  c,  for  the  different 
sections. 

URANYL  NITRATE. 


a. 

b. 

e. 

Bissectrice  aigue"  

A  4870  to  X  4840 

A  4725  to  A  4666 

X  4568  to  X  4525 

Axe  moyen  

A  4698  to  A  4660 

A  4555  to  A  4520 

Bissectnce  obtuse  

A  4864 

A  4695 

A  4551 

The  wave-lengths  of  the  absorption  bands  of  crystals  of  the  double 
chloride  of  uranyl  and  potassium  were  as  follows: 


Bissectrice  aigue  

A  5007 
A  5000 
A  5000 

A  4905       .... 
A  4935  to  A  4920 
A  4953  to  A  4910 

A  4957 

Axe  moyen  

A  '5  04  7 

Bissectrice  obtuse  

A  4843 
A'4826 

A  4783 
A4783 

A  4741 
A  4741 
A  4741 

A4702 
A  4702 

Axe  moyen  

A  4869 
A  4869 

Bissectrice  obtuse  

Knoblauch  *  investigated  the  effect  of  change  of  concentration  on  the 
absorption  spectra  of  various  uranyl  salts.  He  kept  the  amount  of  salt 
in  the  path  of  the  beam  of  light  constant  but  varied  the  concentration 
between  wide  limits.  In  the  case  of  uranyl  nitrate,  UO2(NO,)2-6H2O,  he 
compared  the  absorption  of  solutions  having  concentrations  about  1.1 
normal  (cj  and  0.0033  normal  (c2)  (c,  :  c,  =  3428  :  1).  If  the  molecules 
of  uranyl  nitrate  had  acted  like  the  molecules  of  a  gas,  the  concentrated 
solution  would  have  exerted  a  pressure  of  25.4  atmospheres  and  the  dilute 
solution  Tfa  atmosphere.  For  both  solutions  the  a  (^  4920-4850)  and  the 
6  (>l  4780-4680)  bands  appeared  in  the  same  position.  With  uranyl  acetate, 
UO2(C2H3O2)22H;{O,  a  change  in  concentration  of  cl  :  c2  =  446  :  1  did  not 
cause  any  shift  in  the  a  (A  4940-4870)  or  the  6  (/I  4820-4730)  bands.  The 
position  of  the  edge  of  the  ultra-violet  absorption  was  the  same  for  both 
concentrations.  The  absorption  bands  were  found  to  be  more  intense  for 
the  dilute  solution.  Uranyl  chloride  in  concentrations  cl  :  c2  =  2500  :  1 


Loc.  cit. 


URANIUM    SALTS. 


87 


showed  three  absorption  bands,  a  (/I  4950-4870),  b  (A  4820-4720) ,  and  c 
0*  4650-4560).  The  bands  were  unaffected  by  dilution. 

Knoblauch  considers  that  deviations  from  Beer's  law  must  be  due  to 
(1)  a  change  in  the  molecular  complex  that  constitutes  the  absorber;  (2)  a 
chemical  change  such  as  hydrolysis  or  hydration;  (3)  dissociation;  (4) 
mutual  actions  which  exist  between  the  dissolved  molecules  in  concentrated 
solutions  that  do  not  occur  in  very  dilute  solutions.  The  experimental 
results  which  he  obtains  for  uranyl  and  eosin  salts  indicate  that  deviations 
from  Beer's  law  can  not  be  explained  as  being  due  to  dissociation. 

Hartley  has  made  an  interesting  observation  on  uranyl  nitrate,  UO2- 
(N03)2.6H2O.  He  finds  on  dissolving  this  crystalline  nitrate  in  ether  that 
the  water  of  crystallization  does  not  act  as  ordinary  water  and  mix  with 
the  ether,  but  that  it  remains  in  combination  with  the  uranyl  nitrate.  It 
would  be  interesting  to  find  the  effect  of  change  in  temperature  on  this 
water.  In  this  connection  it  is  very  important  to  determine  the  trans- 
ference numbers  for  the  various  uranyl,  uranous,  and  neodymium  salts  in 
different  solvents  and  mixtures  of  these  solvents.  The  amount  of  heat 
absorbed  or  given  off  when  salts  containing  a  different  number  of  molecules 
of  the  solvent  of  crystallization  are  dissolved  should  also  be  determined. 
These  data  are  necessary  in  order  that  the  facts  obtained  by  spectrum 
analysis  may  be  properly  interpreted.  In  the  case  of  uranium  or  neodym- 
ium it  is  probable  that  only  a  few  of  the  atoms  are  concerned  with  the 
absorption,  and  the  condition  of  the  great  mass  of  the  atoms  may  differ 
very  greatly  from  that  of  the  few  that  are  taking  part  in  the  absorption  of 
light. 

Deussen  *  has  made  a  very  complete  examination  of  the  absorption 
spectra  of  various  uranyl  salts  in  different  solvents  and  in  mixtures  of  dif- 
ferent solvents.  Below  are  the  wave-lengths  measured  by  Deussen: 

URANYL  NITRATE. 


Solvent. 

a. 

b. 

c. 

d. 

e. 

/. 

a- 

A. 

t. 

/. 

Water  .  .  . 

4860 

4720 

4540 

4380 

4290 

4150 

4020 

3870 

3790 

3690 

Ethyl  alcohol  
Methyl  alcohol  .  .  . 
Acetone  .  . 

4845 
4850 
4845 

4680 
4680 
4680 

4490 
4490 
4490 

4360 
4360 
4360 

4240 
4295 
4240 

4090 
4050 
4090 

3990 
4000 
3990 

3840 
3840 
3855 

3750 
3750 
3760 

3660 
3660 
3670 

Glycerol  

4870 

4735 

4525 

4350 

4220 

4060 

3910 

3820 

3710 

Amyl  alcohol  
Acetic  ester  
Ether  

4845 
4850 
4850 

4680 
4685 
4685 

4490 
4495 
4495 

4360 
4365 
4370 

4240 
4250 
4255 

4090 
4095 
4100 

3990 
3995 
4000 

3840 
3845 
3850 

3750 
3755 
3760 

3660 
3665 
3670 

The  above  wave-lengths  of  the  bands  do  not  agree  very  well  with  our 
own  measurements.  For  instance,  the  ethyl  alcohol-bands  are  found  to 
have  a  greater  wave-length  than  the  water-bands.  Deussen  worked  with 
mixtures  of  all  the  above  solvents  and  water.  He  obtained  some  very 
remarkable  results.  For  example,  he  finds  that,  as  compared  with  a  pure 
aqueous  solution  of  uranyl  nitrate,  in  the  50  per  cent  ethyl  alcohol  solution 
all  the  uranyl  bands  are  shifted  towards  the  red.  When  the  solvent  con- 


1  Loc.  ctt. 


88 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 


tains  80  per  cent  alcohol  all  the  bands  are  shifted  towards  the  violet,  and 
for  a  pure  alcohol  solution  all  the  uranyl  bands  are  of  shorter  wave-length 
than  for  a  pure  aqueous  solution. 

Deussen  obtained  very  interesting  results  for  uranyl  nitrate  in  mixtures 
of  water  and  glycerol.  As  the  percentage  of  glycerol  increases  the  c  and  d 
bands  broaden  and  finally,  for  a  pure  glycerol  solution,  form  but  a  single 
band.  At  the  same  time  all  the  other  bands  are  shifted  towards  the  red. 

URANYL  CHLORIDE. 


Solvent. 

a. 

ft, 

c. 

d. 

0. 

1. 

a. 

h. 

». 

rf 

Water  
Ethyl  alcohol  .  .  . 
Glycerol  

4900 
4910 
4920 

4735 
4745 
4755 

4580 
4595 
4600 

4410 
4425 
4510 

4285 
4305 
4410 

4140 
4200 
4280 

4025 
4080 
4170 

3925 
3990 
4030 

3800 
3870 
3940 

3710 
3750 
3810 

3715 

For  uranyl  chloride  solutions  in  mixtures  of  water  and  glycerol,  Deus- 
sen finds  that  the  c  band  of  the  aqueous  solution  breaks  into  two  bands 
when  the  solvent  is  pure  glycerol.  Increasing  percentages  of  glycerol  cause 
an  increased  shift  of  the  bands  towards  the  red. 

URANYL  SULPHATE  (UO2S04.3H»O). 


Solvent. 

a. 

b. 

c. 

d. 

e. 

f. 

a- 

h. 

Water  

4885 

4725 

4560 

4410 

4310 

4180 

4060 

3950 

Ethyl  alcohol  
Glycerol  

4890 
4890 

4730 
4730 

4565 
4570 

4420 
4430 

4320 
4340 

4190 
4210 

4070 
4090 

3960 
3980 

H.  Becquerel1  has  made  a  number  of  observations  on  the  absorption 
spectra  of  uranium  compounds  at  low  temperatures.  He  considers  that 
the  absorption  and  phosphorescent  bands  are  parts  of  a  single  system. 
They  have  two  bands  in  common.  He  states  that  any  modification  in  the 
appearance  of  one  set  of  bands  for  any  compound  is  reproduced  by  a  similar 
change  in  the  other  set  of  bands.  In  general,  the  bands  found  at  the  tem- 
perature of  liquid  air  are  moved  towards  the  violet  with  respect  to  the  same 
bands  at  ordinary  temperatures.  Uranyl  nitrate,  at  ordinary  tempera- 
tures, gives  wide  diffuse  bands  whose  intensities  are  at  a  maximum  at 
their  middle.  At  the  temperature  of  liquid  air  each  group  is  resolved  into 
several  centers,  and  the  most  intense  of  these  bands  are  towards  the  violet. 
A  table  of  the  wave-lengths  of  these  bands  is  given  below. 

Bois  and  Elias  2  find  that  the  double  sulphate  of  uranyl  and  potassium 
when  cooled  to  - 190°  gives  bands  at  AA  4878,  4882,  4888,  and  4905.  These 
seem  to  broaden  slightly  when  placed  in  a  strong  magnetic  field.  At  18° 
uranyl  nitrate  gives  bands  at  A  4675-4716,  /I  4849^880,  and  at  - 190°  C. 
strong  bands  at  A  4679-4697,  A  4845-4849,  and  X  4853^857. 

Uranous  salts  are  of  a  deep  green  color  and  have  a  very  characteristic 
absorption  spectrum,  which  consists  of  diffuse  bands  scattered  throughout 


'Compt.  rend.,  101,  1252  (1885);  144,459,  671  (1907). 
1  Ann.  Phys.,  27,  299  (1908). 


URANIUM    SALTS. 


the  spectrum.  With  the  exception  of  a  short  description  of  a  few  of  the 
bands  by  Formanek,  practically  nothing  has  been  done  on  the  absorption 
of  uranous  salts  either  in  solution  or  in  the  crystalline  condition. 


Crystals  of  uranyl  nitrate. 

Double  sulphate  of  uranyl  and 
potassium. 

Double  chloride  of  uranyl  and 
potassium. 

Room 
temperature. 

Liquid  air. 

tem^Ture.           "*•"•* 

Room 
temperature. 

Liquid  air.     j 

Diffuse  band. 

6500 

6400-6360 

6360 

6270 

6315 

6360 

6170(s) 

6185-6175 

6201-6150 

6145-6127 

6155  weak    j    6155-6145(s) 

6104 

I    6039-5945 

6055 

6030(s) 

6050 

5800 

5910(f) 

5970-5975 

5751  (B) 

5856(8) 

5890-5885    |    5887(s) 

5920 

5833(s) 

5830 

5776-5740(s) 

5721  (f) 

5782 

5763 

5702(f) 

5707 

5760 

5715 

5632(t) 

5619(f) 

5630 

5695-5674 

5515-5481(8) 

5555(f) 

5600 

5647(s) 

5447 

5535 

5580(s) 

5610-5560 

5616(s) 

5394(f) 

5486(s) 

5553(s) 

5591  (s) 

5275-5247(s) 

5462(f) 

5490 

5535 

5886 

5205 

5435(t) 

5435 

5515 

5410 

5161  (f) 

5400(f) 

5375 

5427(t) 

51l6(f) 

5373(f) 

5323(s) 

5384(f) 

5080(t) 

5361  (f) 

5297(s) 

5365(s) 

5065(t) 

5315(f) 

5272 

5347 

5042 

5295(8) 

5240 

5338(s) 

4995 

5224(s) 

5190 

5334 

5202(f) 

5137 

5138 

5156(f) 

5120-5060 

5115 

5124(f) 

5196(f) 

!    5093(s) 

5114(s) 

5072 

j    5072(s) 

5000 

5040(s) 

5018 

4932(s) 

5012 

4893^855 

4975 

4910(s) 

4990(f) 

4925 

4900(s) 

; 

THE   ABSORPTION    SPECTRUM   OF   URANYL    CHLORIDE. 

The  absorption  spectrum  of  uranyl  chloride  (crystals  having  the  com- 
position. UO2C12.H20  at  ordinary  temperatures)  has  been  mapped  for  solu- 
tions in  water,  methyl  and  ethyl  alcohols,  in  mixtures  of  these  solvents  and 
in  solutions  with  aluminium  and  calcium  chlorides  and  for  the  anhydrous 
salt. 

URANYL  CHLORIDE  IN  AQUEOUS  SOLUTIONS. 

The  absorption  spectrum  (Plate  48,  B)  of  uranyl  chloride  in  water  was 
mapped  for  1,  0.75,  0.50,  0.33,  0.25,  0.16,  and  0.125  normal  solutions,  the 
depth  of  layer  being  3  mm.  and  the  time  of  exposure  to  the  Nernst  glower 
with  a  current  of  0.8  ampere  being  1  minute.  The  slit-width  was  0.08  mm. 

The  absorption  spectra  of  the  chloride  and  bromide  are  very  similar, 
the  blue-violet  absorption  band  being  slightly  stronger  for  the  chloride. 
The  uranyl  bands  are  very  broad  and  diffuse  for  both  salts,  being  slightly 


90  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

more  diffuse  for  the  chloride.  Practically  only  the  a,  b,  and  c  bands  appear 
with  any  strength. 

Of  these,  a  and  6  are  the  stronger.  They  appear  of  about  the  same 
intensity  and  are  about  80  Angstrom  units  wide.  For  the  bromide  a  is 
considerably  weaker  than  6.  The  sulphate  and  nitrate,  on  the  other  hand, 
show  practically  all  of  the  uranyl  bands,  the  bands  being  the  strongest  in 
the  sulphate  solution.  In  this  salt  solution  the  6  and  c  bands  are  six  to 
ten  times  as  strong  as  the  a  band.  In  the  nitrate  this  difference  is  not  so 
marked,  and  the  bands  appear  somewhat  finer  than  in  the  case  of  any 
other  salt.  The  acetate  shows  the  greatest  absorption  of  the  salts  men- 
tioned above.  Here,  the  a,  6,  and  c  bands  are  very  faint.  About  half  a 
dozen  very  faint  bands  appear  together. 

For  the  normal  solution  the  ultra-violet  and  blue-violet  bands  merge 
together  and  end  at  ^  4550.  For  the  0.75  normal  solution  the  blue-violet 
band  is  limited  by  regions  of  absorption  beyond  the  limits  M  4500  and 
3900,  for  the  0.5  normal  solution,  U  4470  and  3950,  and  for  the  0.33  normal 
solution,  ;U  4400  and  4050,  the  center  of  the  band  thus  being  at  A  4200. 
Collecting  the  results  of  their  measurements  of  the  center  of  this  blue- 
violet  band  we  have: 

Uranyl  chloride A  4200 

Uranyl  nitrate X  4150 

Uranyl  bromide X  4250 

Uranyl  acetate X  4200 

Uranyl  sulphate A  4180 

Therefore,  for  all  these  salts  the  blue-violet  bands  appear  at  the  same 
position. 

The  band  also  widens  with  increase  in  concentration  quite  uniformly. 
The  edges  of  the  ultra-violet  band  are:  0.75  normal  X  3700,  0.5  normal 
>t  3670,  0.33  normal  A  3650,  0.25  normal  X  3630,  0.16  normal  A  3600,  and 
0.125  normal  I  3570. 

The  positions  of  three  of  the  uranyl  bands  (a,  b,  and  c)  were  measured. 
On  account  of  the  extreme  faintness  of  c  the  result  for  this  band  is  not  very 
accurate:  a,  4920;  6,  4740;  c,  4560;  d,  4460;  e,  4315;  /,  4170;  g,  4025. 

In  addition  to  the  bands  already  given,  uranyl  chloride  has  several 
remarkably  fine  bands  in  the  green.  These  bands  are  not  more  than  5  Ang- 
strom units  wide  and  were  first  seen  on  spectrograms  made  on  the  Wratten 
and  Wainwright  red-sensitive  films.  They  appear  only  for  aqueous  solu- 
tions of  uranyl  chloride.  The  addition  of  calcium  or  aluminium  chloride 
causes  them  to  disappear.  They  do  not  appear  in  the  alcoholic  solutions. 
Uranyl  sulphate  shows  the  same  bands  at  about  the  same  position  as  the 
chloride  but  much  weaker — too  weak  to  be  separated.  The  wave-lengths 
are  as  follows:  >U  5185,  5200,  6000,  6020,  6040,  and  6070. 

So  far  as  the  writers  know,  this  is  the  first  time  that  these  bands  have 
been  noticed  in  aqueous  solutions.  Uranyl  salts  give  a  spectrum  of  emis- 
sion through  phosphorescence,  and  this  spectrum  appears  to  be  a  continua- 
tion of  the  absorption  spectra  to  longer  wave-lengths.  Becquerel l  has 

1  Mem.  Acad.  Sci.,  40  (1872). 


URANIUM    SALTS.  91 

found  that  any  uranyl  compound  showing  a  modification  of  the  absorp- 
tion bands  shows  a  similar  modification  of  the  emission  phosphorescent 
bands. 

A  series  of  spectrograms  was  made  to  test  Beer's  law.  Exposures 
were  made  under  the  standard  conditions  with  1,  0.75,  0.5,  0.33,  0.25,  0.16, 
and  0.125  normal  solutions  of  uranyl  chloride,  the  corresponding  depths  of 
cell  being  3,  4,  6,  9,  13,  18,  and  24  mm. 

There  is  a  slight  transmission  band  in  the  ultra-violet  between  the 
blue-violet  and  ultra-violet  bands.  This  transmission  region  is  roughly 
100  Angstrom  units  wide,  and  is  so  faint  that  it  does  not  appear  upon  the 
printed  plates.  This  band  obeys  Beer's  law.  The  long  wave-length  edge 
of  the  blue-violet  absorption  band,  however,  deviates  slightly  from  Beer's 
law.  For  the  1,  0.75,  0.5,  and  0.33  normal  solutions  the  absorption  is 
slightly  greater  than  for  the  0.25  normal  solution.  The  0.25,  0.16,  and 
0.125  normal  solutions  obey  Beer's  law.  The  edge  for  the  1  normal  solu- 
tion is  roughly  75  Angstrom  units  nearer  the  red  than  for  the  0.25  normal 
solution.  The  uranyl  bands  a  and  6  are  slightly  stronger  for  the  more 
concentrated  solutions.  A  similar  run  for  Beer's  law  was  made  between 
the  concentrations  0.125  and  0.0156  normal.  Beer's  law  holds  in  this 
case,  the  absorption  being  complete  for  wave-lengths  less  than  A  4150. 
The  uranyl  bands  do  not  appear  at  all. 

URANYL,  CALCIUM,  ALUMINIUM,  AND  ZINC  CHLORIDES  IN  WATER;  URANTL  CHLORIDE  AND 
HYDROCHLORIC  ACID  IN  WATER. 

Plate  52,  A  and  B.  were  taken  for  aqueous  solutions  of  uranyl  chloride 
of  a  constant  concentration  to  which  varying  amounts  of  calcium  chloride 
were  added.  The  addition  of  calcium  chloride  causes  the  ultra-violet,  the 
blue-violet,  and  the  uranyl  bands  to  widen  generally.  The  effect  upon  the 
uranyl  bands  is,  however,  very  small.  The  effect  of  aluminium  chloride, 
shown  in  Plate  51,  A  and  B,  on  the  other  hand,  is  very  great.  The  two 
narrow  and  faint  bands  at  X  5200  appear  only  in  the  pure  aqueous  solution 
of  uranyl  chloride.  The  a  band  in  the  aqueous  solution  is  about  60 
Angstrom  units  wide,  and  is  almost  as  intense  as  the  b  band.  The  addi- 
tion of  aluminium  chloride  causes  the  band  to  become  quite  narrow,  about 
25  Angstrom  units  wide.  A  slight  addition  of  aluminium  chloride  decreases 
the  intensity  of  the  band  very  considerably.  Further  increases  in  the 
amount  of  aluminium  have  very  little  effect.  The  addition  of  aluminium 
chloride  also  causes  the  bands  to  shift  to  the  red,  the  shifts  in  some  instances 
amounting  to  25  Angstrom  units.  The  intensity  of  the  6  and  c  bands  is 
very  greatly  increased  by  the  addition  of  aluminium  chloride;  and  by  mak- 
ing the  solution  about  2  normal  with  aluminium  chloride  these  bands  are 
shifted  about  30  Angstrom  units  to  the  red  as  compared  with  the  same 
bands  for  the  pure  uranyl  chloride  solution.  The  d,  e,  f,  g,  and  h  bands 
are  also  increased  in  intensity,  but  are  only  very  slightly  shifted  to  the  red. 
The  d  and  e  bands  are  widened  so  that  they  form  practically  a  single  band. 

In  order  to  bring  out  the  similarity  of  the  action  of  aluminium  chloride 
on  uranyl  and  on  uranous  chlorides,  the  absorption  spectra  of  a  0.2  normal 
solution  of  uranyl  chloride  in  water  (Plate  49,  A),  and  of  a  0.2  normal 


92 


A    STUDY    OP   THE    ABSORPTION    SPECTRA. 


solution  of  uranyl  chloride  and  a  2.4  normal  solution  of  aluminium  (Plate 

49,  B)  were  made.    The  depths  of  layer  were  3,  6,  12,  24,  and  35  mm.    In 
our  discussion  of  the  uranyl  salts  the  effect  of  aluminium  chloride  was 
described.    The  different  effect  of  the  aluminium  chloride  upon  the  a  and  6 
bands  is  very  marked.    In  the  uranous  solution  the  a  band  does  not  appear, 
and  in  fact  the  bands  here  do  not  seem  to  coincide  very  well  either  in  posi- 
tion or  intensity  with  the  bands  of  uranyl  chloride  in  water.    The  position 
of  the  uranyl  bands  when  aluminium  chloride  is  added  is:     a,  4950;    6, 
4790;  c,  4620;  d,  e,  4480-4420;  /,  4270;  g,  4135;  h,  4010. 

(1)  In  uranyl  chloride  in  aqueous  solutions  the  addition  of  aluminium 
chloride  makes  the  uranyl  bands  much  stronger.     It  causes  the  d  and  e 
bands  to  come  together  to  form  practically  one  band. 

(2)  In  aqueous  solutions  of  uranous  chloride  the  addition  of  aluminium 
chloride  before  the  uranyl  salt  was  produced  causes  the  uranyl  bands  to 
appear,  the  position  of  these  bands  being  the  same  as  in  case  1. 

(3)  The  presence  of  aluminium  chloride  in  both  cases  causes  a  greater 
ultra-violet  absorption. 

The  effect  of  hydrochloric  acid  and  zinc  chloride  on  the  uranyl  bands 
is  very  similar  to  that  of  aluminium  chloride. 

Solutions  of  0.2  normal  concentration  were  made  in  very  strong  hydro- 
chloric acid  and  zinc  chloride  solutions.  These  are  represented  by  Plate 

50,  A  and  B.    The  four  spectrograms  (Plates  49  and  50,  A  and  B),  were  all 
made  under  the  same  condition.     Zinc  chloride,  hydrochloric  acid,  and 
aluminium  chloride   have  the   common   property  of   making  the  uranyl 
bands  much  stronger.    Hydrochloric  acid  and  aluminium  chloride  increase 
the  ultra-violet  absorption  and  cause  the  uranyl  bands  to  shift  much  more 
towards  the  red  than  zinc  chloride  does.     The  following  table  gives  the 
wave-lengths  of  the  uranyl  bands  in  aqueous  solutions  when  the  above 
named  substances  are  added: 


a. 

b. 

c. 

d. 

e. 

f. 

°' 

*' 

4. 

Pure  UO-A  

+  ZnCl  3 

4920 
4930 

4740 
4770 

4560 
4600 

4460 
f  4400 
•!  very 

4315 

4170 
4245 

4025 
4115 

.... 

.... 

+  A1C1. 

4950 

4790 

4620 

[  wide 
4480 

4420 

4270 

4135 

4010 

+  HC1  

4950 

4800 

4635 

4480 

4420 

4280 

4150 

4015 

The  bands  of  the  aluminium  chloride  and  hydrochloric  acid  solutions 
do  not  coincide,  and  the  relative  displacements  show  very  clearly  when  the 
two  original  films  are  placed  together  so  that  the  spark  lines  coincide.  In 
none  of  these  spectrograms  do  the  "characteristic  "  uranyl  chloride  bands 
appear,  probably  on  account  of  the  large  slit-width. 

The  zinc  chloride  solution  was  made  by  dipping  zinc  in  hydrochloric 
acid  of  the  same  strength  as  was  used  to  make  the  U02C12  solution  in 
hydrochloric  acid.  To  the  zinc  chloride  and  hydrochloric  acid  solutions  a 
normal  solution  of  uranyl  chloride  was  added  so  as  to  make  the  resulting 
uranyl  chloride  solution  0.2  normal. 


URANIUM   SALTS. 


93 


URANYL  CHLORIDE  IN  METHYL  ALCOHOL. 

The  first  spectrogram  for  mapping  out  the  absorption  spectrum  of 
uranyl  chloride  in  methyl  alcohol  is  given  in  Plate  53,  B.  Exposures 
were  made  to  the  Nernst  glower  for  1  minute  with  a  slit-width  of  0.08  mm. 
and  a  current  of  0.8  ampere.  The  depth  of  cell  is  6  mm.  for  each  strip. 
Beginning  with  the  strip  nearest  the  numbered  scale,  the  concentrations 
are  0.0625,  0.079,  0.1,  0.125,  0.158,  0.2,  and  0.25  normal. 

The  alcoholic  solution  of  uranyl  chloride  is  veiy  similar  to  the  alcoholic 
solution  of  uranyl  nitrate,  the  absorbing  power  of  both  solutions  being 
considerably  greater  than  that  of  aqueous  solutions.  The  aqueous  solution 
of  uranyl  chloride  shows  only  a  few  of  the  characteristic  uranyl  bands  in 
its  absorption  spectrum.  In  the  alcoholic  solution,  however,  they  appear 
very  strongly. 

Starting  with  the  most  concentrated  solution,  whose  absorption  spec- 
trum is  given  by  the  strip  furthest  from  the  numbered  scale,  we  have  the 
bands  a  and  b  appearing  and  all  wave-lengths  less  than  ^  4500  completely 
absorbed.  The  b  band  is  very  strong,  the  a  band  very  weak — almost 
lost  in  this  region  of  the  spectrum  where  the  film  is  less  sensitive  to  the 
light.  For  the  next  concentration,  2  normal,  we  have  a  weak  transmis- 
sion band  appearing  in  the  ultra-violet.  Other  uranyl  bands  appear  as 
the  concentration  is  decreased.  We  shall  now  consider  the  blue-violet 
band.  For  the  0.2  normal  solution  its  limits  are  M,  4450  and  3800,  for 
the  0.158  normal  solution  JU  4400  and  3900,  and  for  the  0.125  normal 
solution  M  4350  and  3900.  The  middle  of  the  band  would  thus  come  at 
about  >l  4100. 

The  uranyl  bands  a,  6,  c,  d,  e,  f,  g,  h,  i,  and  /  all  appear.  The  bands 
b  and  c  are  the  largest  and  strongest.  Band  a  is  relatively  much  weaker. 
The  appearance  of  the  bands  is  somewhat  like  the  bands  of  uranyl  nitrate 
in  methyl  alcohol.  The  uranyl  nitrate  bands  are,  on  the  whole,  considerably 
fainter  and  narrower  than  the  uranyl  chloride  bands.  Bands  a,  6,  and  c 
are  almost  of  the  same  intensity  in  the  case  of  the  nitrate,  all  being  quite 
faint.  The  blue-violet  band  is  much  more  diffuse  in  the  spectrum  of  the 
uranyl  nitrate.  The  following  are  the  wave-lengths  of  the  bands  of  uranyl 
chloride,  the  second  row  giving  the  wave-lengths  of  the  same  bands  for 
uranyl  nitrate  in  methyl  alcohol: 


flt. 

b. 

c. 

d. 

e. 

/. 

a. 

h. 

». 

j. 

Chloride  
Nitrate  

4930 
4930 

4760 
4760 

4610 
4610 

4465 
4460 

4345 
4325 

4220 
4190 

4090 
4070 

3980 
3970 

3860 
3855 

3760 

The  a,  b,  and  c  bands  of  the  chloride  and  nitrate  come  at  about  the 
same  positions,  but  the  e,  /,  g,  and  h  bands  of  the  chloride  are  all  shifted 
towards  the  red  as  compared  with  the  same  bands  of  the  nitrate.  The 
uranyl  chloride  bands  in  water  are  slightly  shifted  towards  the  violet  with 
reference  to  the  uranyl  chloride  bands  in  methyl  alcohol. 


94  A    STUDY    OF   THE    ABSORPTION    SPECTRA. 

The  relative  intensities  of  the  bands  do  not  completely  agree  with 
those  given  by  Deussen.1  In  the  main,  the  results  agree  fairly  well  with 
his;  he  finding  that  in  alcohol  the  bands  are  shifted  towards  the  red. 

Plate  55,  A,  was  made  in  exactly  the  same  way  as  Plate  53,  B,  the  only 
difference  being  that  the  depth  of  cell  was  15  mm.  whereas  for  the  spectro- 
gram previously  described  the  depth  of  cell  was  only  3  mm.  This  spec- 
trogram shows  very  well  how  a  uranyl  band  increases  in  intensity  as  the 
edge  of  the  blue-violet  band  approaches  it. 

The  a  band  thus  increases  in  intensity  and  in  width  with  increase  in 
concentration.  The  band  also  seems  to  widen  unsymmetrically,  although 
the  disymmetry  may  be  due  in  part  to  the  unequal  sensitiveness  of  the  photo- 
graphic film  to  different  wave-lengths  of  light  in  this  part  of  the  spectrum. 

The  spectrogram  Plate  53,  A,  taken  to  test  Beer's  law,  was  made  by 
exposures  of  1  minute  to  the  Nernst  glower  with  a  current  of  0.8  ampere, 
and  slit-width  of  0.08  mm.  Exposures  to  the  spark  in  order  to  get  refer- 
ence lines  were  made  only  in  the  ultra-violet.  Starting  with  the  strip  next 
to  the  numbered  scale,  the  concentrations  were  0.0625,  0.079,  0.1,  0.125, 
0.158,  0.2,  and  0.25  normal,  the  corresponding  depths  of  cell  being  24,  19, 
15,  12,  9.5,  7.5,  and  6  mm. 

Beer's  law  holds  for  the  alcoholic  solutions  between  0.25  normal  and 
0.06  normal.  The  limit  of  absorption  is  at  A  4650  and  is  quite  sharp,  this 
being  the  long  wave-length  edge  of  the  uranyl  c  band.  The  6  band  is  very 
strong,  the  a  band  quite  weak. 

A  very  faint  transmission  band  appears  at  A  3850  and  is  about  100 
Angstrom  units  wide.  This  band  also  obeys  Beer's  law  and  is,  in  fact, 
quite  a  sensitive  index  for  any  deviations  from  this  law. 

URANYL  CHLORIDE  AND  CALCIUM  CHLORIDE  IN  METHYL  ALCOHOL. 

Plate  54,  A  and  B. — These  spectrograms,  showing  the  absorption 
spectra  of  mixtures  of  uranyl  chloride  and  calcium  chloride  in  methyl 
alcohol,  were  taken  under  the  same  conditions.  Exposure  was  made  to 
the  Nernst  glower  for  1  minute  with  a  slit-width  of  0.08  mm.  and  a  current 
of  0.8  ampere.  The  ultra-violet  standard  lines  were  photographed  with 
the  uranyl  solution  removed  from  the  light  beam.  In  every  case  the  con- 
centration of  uranyl  chloride  was  0.125  normal.  Starting  with  the  strip 
at  the  top  of  the  spectrogram  of  both  A  and  B  the  concentrations  of  calcium 
chloride  were  0.0,  0.144,  0.0288,  0.432,  0.576,  0.72,  and  0.9  normal.  In  A 
the  depth  of  solution  was  6  mm.,  in  B  3  mm. 

The  effect  of  calcium  chloride  on  the  absorption  spectra  of  a  methyl 
alcohol  solution  of  uranyl  chloride  is  very  slight,  notwithstanding  the 
power  of  calcium  chloride  to  combine  with  alcohol.  An  increased  amount 
of  calcium  chloride  causes  the  ultra-violet  and  blue-violet  bands  to  widen 
slightly,  as  will  be  seen  from  both  A  and  B.  The  change  in  the  intensity 
of  the  uranyl  bands  is  also  very  slight. 

In  the  upper  strip  of  B  appear  the  bands  a,  b,  c,  d,  e,  f,  i,  and  /.  Only 
one  edge  of  a  is  to  be  seen  clearly;  b  and  c  are  clear  and  entirely  separated; 

1  Ann.  Phys.,  66,  1137  (1898). 


URANIUM   SALTS.  95 

d  is  very  diffuse  and  especially  so  on  the  violet  side ;  e  is  also  diffuse  but  is 
a  distinct  band.  /,  g,  and  h  are  distinct  and  entirely  separated;  i  and  j  can 
also  be  noticed.  When  calcium  chloride  is  added  a  very  peculiar  phenome- 
non manifests  itself.  The  bands  d  and  e  come  together  and,  as  far  as  one 
can  tell,  form  a  single  band.  This  causes  the  bands  /,  g,  and  h  to  shift  to 
the  red,  the  other  bands  becoming  too  faint  to  be  recognized.  Measure- 
ments gave  the  following  wave-lengths  for  the  solution  of  uranyl  chloride  in 
methyl  alcohol  itself:  6,  X  4760;  c,  X  4590;  d,  X  4465;  e,  X  4345;  /,  X  4225;  g, 
X  4095;  h,  X  3975;  and  i,  X  3860.  Taking  up  the  solution  containing  a  0.9 
normal  concentration  of  calcium  chloride  we  find  that  the  6  and  c  bands 
have  remained  at  the  same  part  of  the  spectrum.  The  d  and  e  bands  have 
combined  into  one  large,  diffuse  band  whose  position  is  approximately 
X  4420.  The  /,  g,  and  h  bands  are  now  at  XX  4260,  4120,  and  4010, 
respectively. 

A  spectrogram  was  also  taken  under  conditions  identical  in  every  respect 
with  those  in  A  and  B,  except  that  the  depth  of  layer  was  made  15  mm. 
Here  only  the  a  and  6  bands  appeared.  The  6  band  was  very  wide  and 
strong,  the  a  band  very  weak.  In  the  pure  uranyl  chloride  solution  the 
a  band  was  quite  wide.  As  the  amount  of  calcium  chloride  was  increased 
the  band  became  much  narrower,  and  its  center  shifted  from  X  4925  for  the 
pure  uranyl  chloride  solution  to  about  X  4895  for  the  solution  containing  a 
0.9  normal  concentration  of  calcium  chloride.  Whether  this  could  be  ac- 
counted for  as  due  entirely  to  unsymmetrical  narrowing  is  uncertain, 
though  it  seemed  that  its  short  wave-length  edge  was  slightly  shifted 
towards  the  violet. 

URANYL  CHLORIDE  IN  METHYL  ALCOHOL  AND  WATER. 

Since  the  uranyl  chloride  bands  are  different  in  position  in  water 
from  what  they  are  in  methyl  alcohol,  several  spectrograms  were  made  of 
mixtures  of  alcohol  and  water.  A  and  B,  Plate  56,  are  two  examples.  The 
exposures  were  1  minute  to  the  Nernst  glower,  slit- width  0.01  mm.  and 
current  0.8  ampere.  An  exposure  of  1  minute  to  the  spark  was  also  made 
in  the  ultra-violet  with  the  solution  taken  out  of  the  path  of  the  beam  of 
light.  The  top  strip  of  both  A  and  B  represents  a  0.1  normal  solution  of 
uranyl  chloride  in  methyl  alcohol.  In  the  remaining  cases  the  concentra- 
tion of  uranyl  chloride  is  kept  the  same  and  the  depth  of  cell  the  same. 
The  solvent,  however,  contains  more  and  more  water.  The  second  strip  was 
made  using  a  solution  containing  50  per  cent  water,  the  third  40  per  cent, 
the  fourth  32  per  cent,  the  fifth  24  per  cent,  the  sixth  16  per  cent,  and  the 
seventh  8  per  cent  water.  For  A  the  depth  of  cell  was  16.7  mm.,  for  B  6  mm. 

It  will  be  seen  that  a  small  addition  of  water  causes  a  considerable 
decrease  in  the  absorptive  power  of  the  uranyl  chloride.  The  decrease  of 
absorbing  power  is  much  less  after  the  amount  of  water  has  reached  16  per 
cent.  The  pure  alcohol  solution  in  A  does  not  show  any  transmission  in 
the  ultra-violet  at  all.  The  8  per  cent  aqueous  solution  shows  a  slight  trans- 
mission, the  16  per  cent  aqueous  solution  a  somewhat  stronger  transmission. 
Increase  of  water  beyond  this  amount  increases  the  intensity  of  this  band 
very  slightly. 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


The  most  important  effect  of  the  addition  of  water  is  the  reducing  of 
the  intensity  and  changing  the  position  of  the  uranyl  chloride  bands.  In  A, 
the  bands  a  and  b  appear  in  the  pure  alcoholic  solution.  The  6  band  is 
very  intense.  As  the  amount  of  water  is  increased  a  disappears,  only  one 
edge  of  it  being  recognizable  in  a  16  per  cent  aqueous  solution.  6  is  greatly 
reduced  in  intensity  and  is  shifted  towards  the  violet  by  the  addition  of 
water.  B  shows  still  better  this  effect  upon  the  uranyl  bands.  In  the 
alcoholic  solution  the  bands  a,  b,  c,  /,  g,  h,  and  i  appear.  In  the  8  per  cent 
aqueous  solution  b,  c,  d,  e,  f,  g,  h,  i,  7;  in  the  16  per  cent  aqueous  solution 
b,  c,  d,  e,  f,  g,  h,  i,  and  /;  in  the  24  per  cent  aqueous  solution  the  bands 
are  much  weaker  and  in  the  strips  showing  a  greater  amount  of  water  than 
this,  practically  only  b  and  c  are  visible — and  these  two  bands  are  extremely 
faint.  The  greatest  effect  appears  before  the  amount  of  water  is  greater 
than  20  per  cent.  The  general  effect  upon  the  position  of  the  uranyl  bands 
is  quite  remarkable — the  6  and  c  bands  are  shifted  towards  the  violet  with 
increase  of  water,  whereas  the  ultra-violet  bands  appear  to  be  shifted 
towards  the  red. 


Uranyl  chloride  in  — 

a. 

6. 

c. 

d. 

e. 

f. 

o. 

Water  .  .  . 
CH4O  .... 

4920 
4930 

4930 

4900 
4950 

4740 
4760 

4760 

4750 
4790 

4560 
4590 

4590 

4580 
4620 

4460 
4465 

44 

44 
4480- 

4315 
4345 

20 

00 
4420 

4170 
4220 

4260 

4250 
4270 

4025 
4090 

4120 

4100 
4135 

4010 

3980  3860 
4010 

CHC16} 

cuf.o... 

Water  and  A1C1,  .  .  .  . 

URANYL  CHLORIDE  IN  ETHYL  ALCOHOL. 

Plate  58,  B,  represents  the  absorption  spectra  of  an  ethyl  alcohol  solu- 
tion of  uranyl  chloride,  the  depth  of  cell  being  kept  constant  6  mm.  and 
the  concentration  varied.  Starting  with  the  upper  strip  the  concentrations 
were  0.25,  0.2,  0.158,  0.125,  0.1,  0.079,  and  0.0625  normal.  The  strips 
were  each  exposed  1  minute  to  the  Nernst  glower,  slit-width  being  0.08 
mm.,  current  0.8  ampere.  A  comparison  spectrum  was  also  taken,  exposure 
being  in  this  case  1  minute,  the  solution  having  previously  been  removed 
from  the  source  of  light. 

The  spectrogram  shows  the  blue-violet  band  whose  center  is  about 
^  4250  and  also  the  ultra-violet  band.  The  blue-violet  band  gradually 
disappears  when  the  concentration  is  less  than  about  0.10  normal.  The 
uranyl  bands  come  out  quite  strongly,  but  are  not  as  intense  as  in  the 
methyl  alcohol  solution.  The  bands  in  ethyl  alcohol  occupy  the  same 
positions  as  the  uranyl  bands  do  in  a  solution  in  methyl  alcohol  in  which 
there  is  0.9  normal  concentration  of  calcium  chloride.  In  the  0.25  normal 
solution  the  a  band  has  divided  into  two  faint  bands  whose  centers  are 
about  I  5000  and  X  4900;  the  b  band  is  at  ^  4750,  c  at  X  4585,  d  and  e  at 
I  4400,  /  at  ^  4250,  g  at  X  4100,  h  at  A  3985,  and  i  at  /I  3865. 

The  character  of  the  a  band  is  shown  in  A,  Plate  57.  This  spectrogram 
was  taken  under  the  same  conditions  as  A,  Plate  58,  except  that  here  the 
depth  of  cell  was  15  mm.,  whereas  in  the  other  spectrogram  it  was  6  mm. 


URANIUM   SALTS.  97 

A,  Plate  58,  is  a  spectrogram  to  test  Beer's  law,  the  length  of  exposures 
and  concentrations  being  the  same  as  for  B.  Instead  of  the  depth  of  cell 
being  constant,  this  was  changed  so  that  the  product  of  depth  of  cell  and 
concentration  remained  constant.  Beer's  law  was  found  to  hold.  In  this 
spectrogram  the  a  band  is  shown  to  be  broken  up  into  two  other  bands. 
The  a  and  b  bands  also  obey  Beer's  law.  In  the  ultra-violet  there  is  a  faint 
transmission  band.  This  also  is  unaffected  by  change  in  concentration. 

URANTL  CHLORIDE  m  GLYCEROL. 

A  and  B,  Plate  59,  represent  the  absorption  spectra  of  a  solution  of 
uranyl  chloride  in  glycerol,  the  depth  of  cell  being  10  and  5  mm.,  respec- 
tively. The  concentrations,  starting  with  the  strip  nearest  the  scale,  were 
0.176,  0.132,  0.088,  0.059,  0.041,  0.032,  and  0.022  normal.  The  spectro- 
grams are  very  similar  to  those  of  the  other  uranyl  salts.  The  blue-violet 
absorption  band  vanishes  at  about  >l  4300.  The  positions  of  the  uranyl 
bands  are:  a,  5050;  c,  4720;  d,  4540;  e,  4400;  /,  4260;  g,  4140;  h,  4025; 
and  3920. 

The  uranyl  bands  of  a  glycerol  solution  are  quite  broad.  The  same  is 
true  of  the  uranous  bands.  Glycerol  usually  has  the  effect  of  making  the 
bands  less  dense  than  they  appear  for  most  of  the  other  solvents.  In  a  few 
cases  the  bands  are  quite  fine,  however,  as  in  the  case  of  the  erbium  and 
neodymium  salts. 

URANYL  CHLORIDE  IN  MIXTURES  OF  GLYCEROL  AND  METHYL  ALCOHOL. 

Spectrograms  'A  and  B  (Plate  60)  represent  the  absorption  of  a 
solution  of  uranyl  chloride  in  mixtures  of  glycerol  and  methyl  alcohol. 
The  depth  of  cell  for  A  was  25  mm.,  B  3  mm.  The  concentration  of  uranyl 
chloride  was  0.0176  normal.  The  percentages  of  methyl  alcohol  were  0,  15, 
30,  45,  60,  75,  and  90. 

The  general  ultra-violet  absorption  remains  about  the  same  for  the 
various  mixtures  of  the  solvents.  The  uranyl  bands  change  but  slightly, 
the  b,  c,  and  d  bands  being  the  only  ones  that  change.  The  6  band  of  the 
upper  strip  has  a  weak  component  at  ^  4800,  the  c  band  at  K  4660,  and  the 
d  band  appears  double.  The  wave-lengths  of  the  bands  remain  practically 
the  same  as  for  the  pure  glycerol  solution.  The  methyl  alcohol  bands, 
however,  are  quite  different  in  position  from  the  glycerol  bands,  and  from 
these  spectrograms  we  see  that  practically  all  the  change  must  occur 
between  a  90  per  cent  and  a  100  per  cent  methyl  alcohol  mixture;  the 
glycerol  bands  being  much  more  persistent  than  the  alcohol  bands. 

URANYL  CHLORIDE  IN  ACETONE  AND  THE  EFFECT  OF  HYDROCHLORIC  ACID  ON  THE  URANYL 

ACETATE  BANDS. 

A  solution  of  uranyl  chloride  (3  grams  in  100  c.c.  acetone)  was  made 
and  the  absorption  spectra  of  depths  of  layer  of  3,  6,  and  15  mm.  were 
taken.  Depths  of  1.5,  3,  and  9  mm.  were  then  used  of  the  above  acetone 
solution,  to  which  an  equal  volume  of  strong  hydrochloric  acid  had  been 
added.  The  addition  of  hydrochloric  acid  causes  the  solution  to  become 
very  red.  Upon  the  spectrogram  there  were  7  strips.  The  addition  of 
7 


98 


A    STUDY    OP   THE   ABSORPTION    SPECTRA. 


hydrochloric  acid  caused  the  uranyl  bands  to  break  up  into  several  com- 
ponents. It  also  caused  a  very  great  amount  of  increased  absorption 
throughout  the  spectrum.  Strip  1  showed  absorption  of  the  shorter  wave- 
lengths to  X  3800,  strip  3  to  >l  4700,  strip  4  to  X  3700,  strip  5  to  X  4200  (and 
a  broad  diffuse  band  at  X  5100),  strip  6  to  A  6000,  and  strip  7  to  A  6300, 
approximately.  For  the  solution  containing  hydrochloric  acid  the  uranyl 
bands  are  not  as  strong  as  for  the  pure  acetone  solution.  The  wave-lengths 
of  the  uranyl  bands  are  as  follows  (in  acetone) : 


a  4960  to  4930 
6  4795  to  4760 
c  4645n,  4630,  4600 
d  44706 


e  43206 
/  4180 
g  4040 


In  the  pure  acetone  solution  the  o,  b,  and  c  bands  each  contain  two 
bands  of  about  equal  intensity,  that  almost  blend  into  a  single  band.  There 
are  fine  bands  at  /U  4980,  5000,  5030,  5240,  5270,  and  5295. 

URANYL  CHLORIDE  IN  ACETONE  AND  WATER. 

A  spectrogram  was  made  showing  the  way  the  uranyl  bands  of  an 
acetone  solution  are  affected  by  hydrochloric  acid  and  water.  Strip  1  is 
the  absorption  of  a  2  mm.  solution  of  0.0088  normal  uranyl  chloride  in 
acetone;  strip  2  is  the  same  to  which  hydrochloric  acid  has  been  added  so 
as  to  make  a  depth  of  cell  of  3.2  mm.;  strip  3,  where  water  has  been  added 
to  make  a  depth  of  cell  of  3.4  mm. ;  strip  4  to  4  mm. ;  strip  5  to  5  mm. ;  and 
strip  6  to  11  mm.  In  the  latter  case  a  white  precipitate  was  formed. 

The  addition  of  hydrochloric  acid  causes  the  uranyl  bands  to  break 
into  various  components.  The  addition  of  water  causes  these  components 
to  broaden,  weaken,  and  finally  to  form  very  faint,  diffuse  bands.  As  long 
as  the  components  appear  their  wave-lengths  remain  unchanged  as  water 
is  added. 


a. 

b. 

e. 

d. 

e. 

f. 

0. 

Strip  2 
Strip  5 

4930(20) 

4765(30) 
4770(  H 

4605(30) 
4550(/30) 

4610(  f) 

4470(u>20) 
4430(s20) 
4385(u>20) 

4430C  H 

4340(^20) 
4290(s20) 
4250(t«20) 

4250(  f) 

4205(t»20) 
4160(s20) 
4120(«>20) 

4130fn 

1- 

URANYL  CHLORIDE,  TEMPERATURE  EFFECT. 

A  spectrogram  (Plate  61,  A)  was  made  of  the  absorption  spectrum 
of  a  normal  aqueous  solution  of  uranyl  chloride,  the  depth  of  cell  being 
3  mm.  Exposures  were  made  to  the  Nernst  glower  for  90  seconds  (current 
0.8  ampere  and  slit-width  0.20  mm.).  The  time  of  exposure  to  the  spark 
was  6  minutes.  Starting  from  the  comparison  spectrum,  the  temperatures 
were  6°,  18°,  34°,  52°,  68°,  and  82°. 

At  8°  the  ultra-violet  band  extended  to  X  3550,  the  blue-violet  band 
from  A  4000  to  A  4450.  The  bands  a,  6,  and  c  appeared,  but  the  a  band  is 
very  faint.  The  wave-lengths  of  the  6  and  c  bands  were  U  4565  and  4725. 


URANIUM   SALTS.  99 

At  82°  the  ultra-violet  band  extends  to  1 3700,  and  the  blue-violet 
band  from  ^  3950  to  A  4600.  At  this  temperature  only  the  6  band  appears, 
a  being  very  weak  and  c  completely  merged  into  the  blue-violet  absorption 
band.  The  6  band  is  located  at  A  4755. 

A  spectrogram  (Plate  61,  B)  was  made  of  a  0.0156  normal  aqueous 
solution  of  uranyl  chloride  196  mm.  deep.  Exposures  were  made  to  the 
Nernst  glower  for  30  seconds  (current  0.8  ampere  and  slit-width  0.20  mm.). 
No  exposures  were  made  to  the  spark  except  for  comparison  spectra. 
Starting  with  the  numbered  scale,  the  temperatures  were  6°,  18°,  29°,  44°, 
59°,  71°,  and  79°. 

For  this  concentration  there  is  a  very  slight  temperature  effect.  There 
is  a  very  faint  transmission  band  between  the  ultra-violet  and  blue-violet 
bands.  This  is  extremely  faint  and  is  practically  unaffected  by  tempera- 
ture. The  blue-vio  et  band  widened  slightly  with  rise  in  temperature. 
The  uranyl  bands  in  the  concentrated  solution  were  much  stronger  and 
wider  than  in  the  dilute  solution. 

ABSORPTION  SPECTRUM  OF  ANHYDROUS  URANYL  CHLORIDE. 
The  absorption  spectrum  of  the  anhydrous  chloride  was  photographed 
in  the  same  way  as  that  of  the  anhydrous  nitrate.  The  bands  differ  con- 
siderably from  the  bands  of  the  aqueous  solution,  and  one  cannot  tell  very 
well  whether  they  are  identical  with  the  corresponding  a,  b,  c,  etc.,  bands 
of  the  solution  or  not.  Their  wave-lengths  are  approximately  as  follows: 
U  4950  (narrow),  4860,  4765,  4700,  4615,  4540,  4460,  4320,  4290,  4160,  4050, 
and  3940. 

ABSORPTION  SPECTRUM  OF  URANYL  NITRATE  UNDER  DIFFERENT  CONDITIONS. 
URANYL  NITRATE  IN  AQUEOUS  SOLUTION. 

The  spectrum  of  uranyl  nitrate  in  water  is  a  typical  example  of  the 
uranyl  salts.  With  a  depth  of  solution  of  3  mm.  its  absorption  spectrum 
(Plate  62,  A,  B)  was  investigated  between  concentrations  of  1.5  normal 
and  0.0234  normal.  For  the  1.5  normal  solution  the  absorption  consists  of 
a  band  in  the  blue-violet  and  absorption  throughout  the  ultra-violet  portion 
of  the  spectrum.  As  the  concentration  decreases  the  blue-violet  band 
fills  up  with  transmission,  and  the  ultra-violet  absorption  is  pushed  farther 
and  farther  out  into  the  ultra-violet.  The  blue-violet  band  is  practically 
gone  at  a  concentration  of  0.5  normal,  and  there  is  almost  complete  trans- 
mission throughout  the  ultra-violet  for  concentrations  less  than  0.02  normal. 

During  these  changes  in  concentration  a  large  number  of  bands  about 
50  Angstrom  units  wide  make  their  appearance.  Near  the  edge  of  an  ab- 
sorption band  these  bands  are  relatively  quite  clear.  As  the  absorption 
edge  recedes  from  the  uranyl  bands,  the  general  transmission  is  so  great  as 
to  obscure  them  almost  completely. 

A,  Plate  63,  represents  the  absorption  spectra  of  an  aqueous  solution 
of  uranyl  nitrate  of  different  depths  of  layer.  The  narrow  and  rather  weak 
bands  shown  here  are  the  uranyl  bands.  Twelve  of  these  bands  have  been 
photographed.  Starting  with  the  band  of  longest  wave-length  they  will  be 
designated  by  the  letters  a,  b,  c,  d,  etc.  On  account  of  the  irregularity  of 


100  A    STUDY   OF   THE   ABSORPTION    SPECTRA. 

the  distribution  of  light  in  the  spark-spectrum  and  the  small  intensity  of 
the  uranyl  bands,  the  Nernst  glower  was  used  as  the  source  of  light  in  the 
ultra-violet,  and  long  exposures  were  made.  A  screen  was  used  that  cut 
out  all  wave-lengths  greater  than  X  4200.  A  represents  a  typical  spectro- 
gram of  this  kind.  Starting  with  the  spectrum-strip  at  the  top,  the  con- 
centrations were  1.5,  1.1255,  0.75,  0.5,  0.375,  0.25,  and  0.1875  normal. 
The  slit-width  was  0.08  mm.  and  the  current  through  the  Nernst  glower 
0.8  ampere.  The  spectra  of  wave-lengths  greater  than  A  4300  represent 
the  absorption  of  a  depth  of  layer  of  15  mm.;  the  spectra  of  shorter  wave- 
lengths represent  the  absorption  of  a  depth  of  layer  of  3  mm.  The  upper 
spectrum-strip  represents,  then,  the  absorption  spectrum  of  a  1.5  normal 
solution  of  uranyl  chloride  15  mm.  thick,  exposure  to  the  Nernst  glower 
having  been  1  minute.  It  will  be  seen  that  the  uranyl  band  a  comes  out 
very  strongly.  The  screen  was  then  placed  in  the  path  of  light  and  expo- 
sure of  5  minutes  made  to  the  violet  and  ultra-violet  beyond  A  4300;  a  solu- 
tion of  uranyl  nitrate  of  1.5  normal  concentration  and  3  mm.  deep  being 
in  the  path  of  the  beam  of  light.  This  amount  of  uranyl  nitrate  absorbed 
practically  all  the  light  in  this  region.  A  very  short  exposure  was  after- 
wards made  to  the  spark  in  the  region  X  2600,  in  order  to  get  a  comparison 
spark-spectrum  in  this  region,  so  that  the  wave-lengths  of  the  uranyl  bands 
could  be  measured. 

Throughout  this  work  a  comparison  spark-spectrum  usually  contain- 
ing the  very  strong  line  ^  2478.8  was  photographed  on  each  spectrum-strip. 
In  measuring  the  uranyl  bands  all  measurements  were  made  from  this 
line  as  a  standard,  and  although  the  absolute  wave-lengths  of  the  uranyl 
bands  may  not  be  correct  to  within  20  Angstrom  units,  yet  relatively 
they  are  probably  correct  to  within  less  than  10  Angstrom  units  for  the 
finer  bands. 

The  second  spectrum-strip  from  the  top  represents  in  the  long  wave- 
length end  of  the  spectrum,  the  absorption  of  a  15  mm.  layer  of  a  1.125 
normal  solution  of  uranyl  nitrate  exposed  1  minute  to  the  Nernst  glower. 
The  a  band  appears,  although  not  nearly  as  intense  as  in  the  spectrum- 
strip  above.  The  region  of  shorter  wave-lengths  beyond  X  4300  represents 
the  absorption  of  a  3  mm.  layer  of  a  1.125  normal  solution  exposed  5  min- 
utes to  the  Nernst  glower.  A  very  faint  transmission  is  shown  in  the 
region  >l  3700.  The  ultra-violet  line  X  2478.8  is  shown  in  the  comparison 
spark-spectrum.  The  other  spectrum-strips  were  made  in  a  similar  manner, 
with  the  concentrations  given  above. 

By  this  method  of  exposing,  two  new  bands  were  detected  in  the  ultra- 
violet. In  aqueous  solutions  the  intensities  of  the  bands  are  much  the  same. 
In  other  solvents,  however,  and  for  other  uranyl  salts,  the  relative  intensi- 
ties of  the  bands  change  very  greatly.  For  uranyl  nitrate  crystals  the 
bands  are  even  more  closely  related  to  each  other  than  in  aqueous  solu- 
tions. The  longer  the  wave-length  of  the  band  the  more  intense  and  wider 
it  is  as  a  rule.  The  position  of  the  long  wave-length  bands  in  the  ortho- 
rhombic  uranyl  nitrate  crystals,  UO2(NO3)26H2O,  is  the  same  as  the  posi- 
tion of  the  bands  for  an  aqueous  solution.  The  wave-lengths  of  the  bands 
are  as  follows: 


URANIUM    SALTS. 


101 


Aqueous  solution. 

Aqueous  solution. 

Band. 

Deussen. 

Jones  and 
Strong. 

Crystals. 

Band. 

Deussen. 

Jones  and 
Strong. 

Crystals. 

a 

4860 

4870 

4870 

g 

4020 

4030 

4050 

b 

4720 

4705 

4705 

I 

3870 

3905 

3935 

c 

4540 

4550 

4500-4565 

i 

3790 

3815 

3830 

d 

4380 

4390 

4405 

3690 

3710 

(3720?) 

e 

4290 

4275 

3605 

3600 

f 

4150 

4155 

4170 

I 

.... 

3515 

In  the  original  film  from  which  A,  Plate  63,  was  made  all  of  these  bands 
except  d  could  be  very  distinctly  seen.  The  bands  of  longer  wave-length 
are  slightly  wider.  The  i  band  is  considerably  weaker  than  its  neighboring 
bands. 

Spectrograms  (Plate  64,  A  and  B)  were  made  by  exposing  to  the 
Nernst  filament  for  1  minute  at  0.8  ampere,  the  slit-width  being  0.08  mm. 
The  spark  was  run  about  3  minutes.  In  A  the  concentrations  were  1.5, 
1.125,  0.75,  0.5,  0.375,  0.25,  and  0.1875  normal;  in  B,  0.1875,  0.14,  0.094, 
0.0625,  0.047,  0.0312,  and  0.0234  normal,  starting  in  each  case  with  the 
strip  next  to  the  spark-spectrum.  The  corresponding  depths  of  cell  were 
3,  4,  6,  9,  12,  18,  and  24  mm.  respectively.  In  the  case  of  the  more  concen- 
trated solutions  Beer's  law  was  not  found  to  hold.  In  A  there  appear 
the  two  wide  absorption  bands.  The  large  wave-length  limit  of  the  ultra- 
violet band  is  independent  of  the  concentration  when  the  amount  of  salt 
is  kept  constant,  and  is  located  at  about  ^  3520.  The  blue-violet  band  on 
its  short  wave-length  side  also  obeys  Beer's  law  and  ends  at  A  3860.  The 
long  wave-length  edge,  however,  is  pushed  towards  the  red  as  the  concen- 
tration is  increased;  or,  in  other  words,  the  absorption  is  greater  for  a 
given  amount  of  salt  in  concentrated  solutions  than  it  is  in  dilute  solutions. 
The  positions  of  this  edge  for  various  concentrations  are  X  4100  for  0.1875, 
0.25,  0.375,  and  0.5  normal;  A  4150  for  0.75  normal;  >l  4300  for  1.125 
normal;  and  A  4340  for  1.5  normal.  For  B  Beer's  law  holds  and  only  the 
ultra-violet  absorption  band  appears;  its  long  wave-length  side  being  at 
^  3350.  The  intensities  of  the  small  bands  are  independent  of  concentra- 
tion as  far  as  one  can  tell  from  the  spectrograms. 

ABSORPTION  SPECTRUM  OF  URANTL  NITRATE  CRYSTALS. 

For  the  aqueous  solution  there  is  no  sign  that  the  bands  can  be  broken 
up.  In  the  spectrum  of  the  crystal  this  is  not  the  case.  The  a  band  is 
narrow.  The  6  band  is  also  very  narrow,  about  15  Angstrom  units  wide. 
A  very  faint  band  appears  about  A  4650.  The  c  band,  on  the  other  hand, 
is  very  wide,  about  70  Angstrom  units,  and  is  probably  double.  The  d 
band  is  about  50  Angstrom  units  wide,  and  the  e  band  is  about  70 
Angstrom  units  wide  and  appears  double.  The  /  band  is  the  most  intense 
and  is  about  40  Angstrom  units  wide.  The  bands  g,  h,  i,  and  j  keep  de- 
creasing in  intensity  respectively.  The  description  is  of  a  spectrogram 
taken  of  a  crystal  in  Canada  balsam,  and  of  course  the  width  of  the  bands 
varies  with  the  time  of  exposure  and  various  other  things,  but  many  details 


102  A   STUDY   OF   THE    ABSORPTION    SPECTRA. 

are  shown  that  are  not  exhibited  in  other  spectrograms.  It  will  thus  be 
seen  that  the  a,  b,  c,  d,  j,  and  A;  bands  of  the  solution  agree  fairly  well  with 
those  of  the  crystal,  and  that  the  crystal  bands  /,  g,  h,  and  i  are  shifted 
towards  the  red  with  reference  to  the  bands  in  the  aqueous  solution. 

EFFECT  OF  DILUTION  ON  THE  URANYL  BANDS. 

The  effect  of  dilution  on  the  position  and  intensity  of  the  blue-violet, 
the  ultra-violet,  and  the  uranyl  bands  of  the  acetate,  nitrate,  and  sulphate 
of  uranyl  in  water  was  tried.  The  absorption  spectra  of  solutions  about 
1  normal  and  3  mm.  deep  were  photographed  along  by  the  side  of  the  absorp- 
tion spectra  of  0.008  normal  solutions  of  the  same  salts  380  mm.  deep. 
The  absorption  consisted  of  the  blue-violet  band,  the  ultra-violet  band,  and 
the  a,  b,  c,  i,  /,  and  k  bands.  Between  the  blue-violet  and  ultra-violet 
bands  there  was  the  transmission  band  containing  i,  j,  and  k.  For  each 
of  the  three  salts  this  transmission  band  was  much  weaker  for  the  dilute 
solution,  whereas  in  the  cases  of  the  sulphate  and  nitrate  the  long  wave- 
length transmission  edge  of  the  blue-violet  band  was  stronger  for  the  more 
dilute  solution.  The  opposite  was  true  of  the  acetate  solution.  In  the 
dilute  solution  of  the  acetate  the  bands  were  more  intense  than  for  the 
more  concentrated  solution.  There  was  no  noticeable  change  in  the  posi- 
tion of  the  bands.  Neither  the  intensity  nor  the  position  of  the  uranyl 
nitrate  or  the  uranyl  sulphate  bands  was  changed  by  the  above  dilution. 

Plate  65,  A,  represents  the  spectrogram  comparing  the  spectra  of  the 
same  amount  of  uranyl  salt  in  a  concentrated  and  in  a  dilute  solution. 
Starting  with  the  strip  adjacent  to  the  numbered  scale  we  have  the  absorp- 
tion spectra  of  a  1.1  normal  solution  of  uranyl  nitrate  in  water,  the  depth 
of  the  cell  being  3  mm.  The  next  spectrogram  is  of  the  same  solution. 
Then  distilled  water  was  poured  into  the  solution  until  the  length  of  column 
was  380  mm.  The  absorption  spectrum  of  this  solution  is  given  in  the 
third  strip.  The  fourth  strip  represents  the  absorption  of  a  0.75  normal 
solution  of  uranyl  sulphate,  the  depth  of  cell  being  4  mm.  The  fifth  strip 
is  for  the  same  solution  diluted  until  the  depth  was  380  mm.  The  sixth 
strip  represents  the  absorption  of  a  0.188  normal  solution  of  uranyl  acetate 
14  mm.  deep.  The  last  strip  is  for  the  same  solution  diluted  to  a  depth  of 
380  mm. 

A  more  detailed  study  was  made  as  to  whether  Beer's  law  holds  for 
uranyl  nitrate  and  for  the  other  uranyl  salts.  The  method  of  taking  the 
spectrograms  is  the  same  as  that  used  for  the  potassium  salts. 

Beer's  law  was  found  to  hold  for  dilute  solutions  of  uranyl  nitrate  in 
water.  When  the  concentration  is  greater  than  0.5  normal  the  absorption 
is  greater  than  it  should  be  if  Beer's  law  held. 

URANYL  NITRATE  IN  NITRIC  ACID. 

Ordinary  uranyl  nitrate  (UO2(NO3)26H2O)  was  dissolved  in  very  strong 
nitric  acid.  A  spectrogram  (Plate  70,  J5)  was  made  of  this  solution,  differ- 
ent depths  of  cell  being  used. 

The  presence  of  strong  nitric  acid  has  a  very  great  effect  upon  the 
absorption  spectra  of  uranyl  nitrate.  In  general,  it  causes  the  band 


URANIUM   SALTS.  103 

absorption  to  be  very  much  more  intense.  The  bands  are  shoved  towards 
the  violet.  The  a  band,  A  4790,  is  made  very  weak,  the  6  band,  A  4670, 
narrow  and  strong,  the  c  band,  A  4510,  the  d  band,  A  4370,  and  the  e  band, 
>l  4230,  are  quite  strong.  The  other  bands,  /,  A  4125,  g,  A  4000,  h,  A  3900, 
t,  A  3790,  7,  A  3670,  and  k,  A  3570,  are  rather  weak,  the  latter  two  being 
stronger,  however,  than  in  the  corresponding  aqueous  solution. 

When  the  depth  of  layer  is  sufficient  so  that  the  whole  shorter 
wave-length  portion  of  the  spectrum  is  absorbed  to  A  4850,  it  is  found  that 
the  whole  region  of  the  spectrum  remaining  is  filled  with  a  multitude  of 
extremely  fine  absorption  lines. 

This  fine  band  absorption  spectrum  is  that  of  nitric  oxide. 

URANYL  NITRATE  IN  METHYL  ALCOHOL. 

In  a  spectrogram  the  depth  of  cell  was  kept  constant  at  15  mm.;  the 
concentrations,  beginning  with  the  strip  nearest  the  scale,  were  .20,  .158, 
.124,  .10,  0.079,  0.063,  and  0.05  normal.  Exposure  was  made  to  the  Nernst 
glower  for  1  minute  with  the  current  at  0.8  ampere.  The  corresponding 
limits  of  absorption  are  AA  4800,  3750,  3700,  3650,  3600,  3550,  and  3500. 
Two  of  the  smaller  bands,  a  and  b,  appear  at  the  lower  concentration. 
These  bands  are  about  30  Angstrom  units  wide  and  their  positions  are 
AA  4920  and  4745. 

Plate  67,  B,  represents  the  same  concentrations,  0.2  normal,  as  Plate 
54,  A.  Here  the  depth  of  cell  is  kept  constant  at  3  mm.  The  spectro- 
gram shows  the  characteristic  blue-violet  band  and  the  ultra-violet  band. 
For  concentration  0.2  normal,  the  positions  of  the  edge  of  the  ultra-violet 
band  are  AA  3825,  3800,  3770,  3750,  3720,  3700,  and  3670. 

The  blue-violet  band  for  0.2  normal  solution  has  the  limits  A  4470  and 
A  3825.  The  middle  of  this  band  thus  comes  at  about  A  4150;  exactly  where 
the  band  for  water  is  situated.  The  concentration  when  the  same  band 
fades  out  for  water  is  0.5  normal,  whereas  for  alcohol  it  is  much  less,  show- 
ing that  uranyl  salts  in  alcohol  are  much  more  deeply  colored  than  in  water. 
The  following  are  the  wave-lengths  of  the  small  bands:  a,  A  4930;  6,  A 4760; 
c,  A  4610;  d,  A  4460;  e,  A  4325;  /,  A  4190;  g,  A  4070;  h,  A  3970;  i,  A  3855. 

For  Plate  67,  A,  the  Nernst  glower  was  run  1  minute  at  0.8  ampere, 
slit-width  0.08  mm.  Starting  with  the  comparison  spectrum  the  concentra- 
tions were  normal  0.2,  0.16,  0.126,  0.1,  0.08,  0.063,  and  0.033,  the  corre- 
sponding depths  of  solution  being  6,  7.5,  9.5,  12,  15,  19,  and  24  mm.  Uranyl 
nitrate  in  methyl  alcohol  shows  very  marked  deviations  from  Beer's  law, 
the  absorption  being  much  greater  where  the  concentrated  solutions  are 
used.  The  limits  of  absorption  for  concentrations  0.2,  0.16,  0.126,  0.1, 
0.08,  0.063,  and  0.033  normal  are,  respectively,  AA  4720,  4700,  4680,  4660, 
4650,  4640,  and  4630. 

URANYL  NITRATE  IN  METHYL  ALCOHOL  AND  WATER. 

In  the  previous  work  of  Jones  and  Anderson  it  was  found  that  in  the 
case  of  neodymium  salts  the  absorption  spectrum  was  very  often  different 
in  pure  alcohol  from  what  it  was  in  pure  water.  This  fact  had  been  noticed 
before  by  several  observers,  and  had  been  believed  by  some  to  be  due  to  the 


104 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


different  dielectric  constant  of  the  two  different  solvents.  According  to 
such  a  theory  the  bands  should  gradually  shift  in  position  as  one  solvent 
was  increased  and  the  other  decreased  in  amount.  Jones  and  Anderson, 
however,  found  this  not  to  be  the  case.  They  showed  that  there  was  a 
definite  set  of  methyl  alcohol-bands  and  a  definite  set  of  water-bands.  As  the 
amount  of  alcohol  was  decreased  in  a  solution  the  alcohol-bands  weakened  but 
remained  in  the  same  position.  As  the  amount  of  water  was  increased  the 
intensity  of  the  water-bands  increased,  but  they  remained  in  the  same  position. 
These  results  were  interpreted  by  them  as  being  due  to  definite  alcoholates  and 
hydrates— that  a  definite  alcoholate  of  neodymium  had  a  characteristic 
absorption  spectrum.  Recent  work  by  E.  E.  Reid  (Am.  Chem.  Jour.,  June, 
1909)  supports  this  theory.  It  should  also  be  noticed  that  in  general  the 
alcohol-bands  are  on  the  red  of  similar  water-bands. 

One  of  the  purposes  of  the  present  work  was  to  find  whether  this 
matter  of  a  salt  possessing  a  characteristic  absorption  spectrum  in  different 
solvents  was  general  or  not.  So  far,  it  would  seem  to  hold  for  uranyl 
nitrate.  We  have  seen  that  uranyl  nitrate  bands  in  methyl  alcohol  are  all 
nearer  the  red  end  of  the  spectrum  than  the  corresponding  water-bands. 
This  is  not  in  agreement  with  the  results  of  previous  investigators.  To 
illustrate  this  we  will  give  a  table  from  Deussen's  paper.1 

Absorption  spectra  of  uranyl  nitrate  in  mixtures  of  water  and  methyl  alcohol  (Deussen}. 


Band. 

Water. 

"dffif 

SOperct. 

"8EK1- 

Band. 

Water. 

"dBf 

80  per  ct. 
CH40. 

'"SK,"- 

a 

4860 

4860 

4860 

4850 

f 

4150 

4155 

4150 

4090 

b 

4720 

4720 

4720 

4680 

g 

4020 

4030 

4020 

4000 

c 

4540 

4540 

4540 

4490 

h 

3870 

3875 

3870 

3840 

d 

4380 

4385 

4380 

4360 

i 

3790 

3800 

3790 

3750 

e 

4290 

4295 

4290 

4295 

1 

3690 

3690 

3690 

3660 

The  general  results  of  Deussen  are  very  surprising  indeed.  In  general, 
he  finds  that  by  adding  a  little  alcohol  to  an  aqueous  solution  there  is  a 
slight  shift  of  the  uranyl  nitrate  bands  to  the  red.  The  position  of  the  bands 
then  remains  about  the  same  with  increasing  percentage  of  alcohol  until 
the  solvent  becomes  almost  pure  alcohol,  when  there  is  a  sudden  shift 
towards  the  violet.  In  our  work  we  find  nothing  of  this  kind.  We  find 
that  in  pure  alcohol  the  bands  are  all  shifted  to  the  red  as  compared  with 
the  water-bands.  In  order  to  study  further  these  bands,  and  to  learn 
whether  there  was  a  gradual  shift  from  alcohol-bands  to  water-bands,  or 
whether  the  alcohol-bands  simply  became  fainter  but  remained  in  the 
same  position  while  the  water-bands  became  stronger  while  remaining  in 
the  same  position  as  the  percentage  of  water  was  increased,  a  set  of  solu- 
tions was  made  up  with  varying  amounts  of  water  and  alcohol;  the 
concentration  of  uranyl  nitrate  remaining  constant  at  0.1  normal.  For 
this  purpose,  of  course,  the  anhydrous  uranyl  nitrate  was  used.  Plate  66 
represents  two  of  the  spectrograms.  In  A,  starting  with  the  strip  nearest 
the  spark-spectrum  the  percentages  of  alcohol  were  100,  92,  84,  76,  68,  60, 

1  Ann.  Phys.,  66,  1132  (1898). 


URANIUM   SALTS.  105 

50.  In  B  everything  was  the  same  excepting  the  depth  of  cell  which  was 
6  mm.,  whereas  in  A  it  was  15  mm.  An  exposure  of  1  minute  was  made 
to  the  Nernst  glower  running  with  a  current  of  0.8  ampere.  The  slit-width 
was  0.08  mm. 

The  original  negatives  show  that  the  absorption  is  much  greater  for  the 
pure  alcoholic  solutions  than  for  the  mixtures  with  water.  The  change  from 
the  absorption  of  pure  alcohol  to  a  92  per  cent  solution  is  very  marked. 
The  plates  show  that  in  mixtures  of  alcohol  and  water  the  bands  are  very 
broad,  and  that  these  broad  bands  are  certainly  the  water-  and  alcohol-bands 
coexisting.  Their  combination  causes  the  banded  appearance  of  the  spec- 
trum to  be  so  weak  that  no  measurements  were  made. 

URANYL  NITRATE  IN  ETHYL  ALCOHOL. 

The  general  absorption  of  uranyl  nitrate  in  ethyl  alcohol  is  similar  to 
the  absorption  in  methyl  alcohol.  Plate  68,  B,  represents  the  absorption  of 
a  15  mm.  solution,  the  concentrations  being  0.2,  0.16,  0.127,  0.10,  0.08, 
0.063,  and  0.033  normal;  the  most  concentrated  solution  being  nearest  the 
comparison  scale.  The  source  of  light  was  the  Nernst  filament  for  1  minute, 
at  0.08  ampere,  with  a  slit  of  0.08  mm.  width.  The  characteristic  wide 
absorption  bands  of  uranyl,  the  blue-violet  and  the  ultra-violet  bands, 
merge  together  in  the  strips  next  to  the  comparison  scale.  They  become 
separated  at  a  concentration  of  0.127  normal.  The  limits  of  the  blue- 
violet  band  are  for  0.1  normal  M  4000  and  4670,  for  0.08  normal  >U  3950  and 
4550,  for  0.063  normal  >U  3900  and  4500,  for  0.033  normal  tt  3950  and  4450, 
the  middle  of  the  band  coming  at  about  X  4200. 

The  characteristic  uranyl  bands  of  the  ethyl  alcohol  solution  are 
extremely  faint,  and  on  this  account  are  hard  to  recognize.  There  is  a 
wide  and  very  faint  band  at  X  5200,  which  is  at  least  50  Angstrom  units 
wide,  and  has  never  been  seen  by  the  authors  for  any  other  uranyl  salt. 
The  band  that  comes  approximately  in  the  position  of  what  we  called 
band  a  is  very  wide,  about  90  Angstrom  units.  Band  6  is  very  faint. 
The  following  are  the  wave-lengths  of  the  various  bands,  and  we  will 
designate  them  by  small  letters;  although  it  is  not  certain  whether  say 
band  c  or  d  corresponds  to  bands  that  we  have  hitherto  designated  in 
this  manner:  a,  5000;  b,  4800;  c,  4630;  d,  4475;  e,  4325;  /,  4175;  g,  4080; 
h,  3970;  i,  3875.  Here  again  we  obtain  entirely  different  results  from 
Deussen.  He  found  that  by  gradually  increasing  the  percentage  of  alcohol 
he  first  obtained  a  shift  of  the  bands  toward  the  red,  and  when  the 
amount  of  alcohol  kept  on  increasing  a  final  shift  towards  the  violet. 

Starting  with  the  comparison  spectrum  in  Plate  68,  A,  the  concentra- 
tions are  0.2,  0.16,  0.127,  0.10,  0.08,  0.063,  and  0.033  normal,  the  corre- 
sponding depths  of  cell  being  6  mm.,  7.5  mm.,  9.5  mm.,  12  mm.,  15  mm., 
19  mm.,  and  24  mm.  From  the  spectrogram  it  is  seen  that  Beer's  law  does 
not  hold,  the  absorption  being  greatest  for  the  most  concentrated  solution. 
This  holds  true  both  for  the  blue-violet  band  and  for  the  ultra-violet  band. 
It  would  be  interesting  to  know  whether  for  the  same  dissociation  Beer's  law 
would  hold  for  water  and  alcohol  solutions;  also  whether  other  properties, 
like  fluidity,  vapor-pressure  lowering,  conductivity,  etc.,  vary  in  the  same  way. 


106 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


URANYL  NITRATE  IN  MIXTURES  OF  GLYCEROL,  WATER,  ACETONE,  AND  ETHYL  ALCOHOL. 
Plate  69,  A  and  B,  represents  the  absorption  of  solutions  25  and  6  mm. 
in  depth,  respectively.  Strip  1  represents  the  absorption  of  a  solution  of 
uranyl  nitrate  in  glycerol;  strip  2  of  3  parts  glycerol  and  1  part  water; 
strip  3  of  2  parts  glycerol  and  2  parts  water;  strip  4  of  1  part  glycerol  and 
3  parts  water;  strip  5  of  1  part  glycerol  and  3  parts  acetone,  and  strip  6  of 
1  part  glycerol  and  3  parts  ethyl  alcohol.  The  concentration  of  uranyl 
nitrate  in  glycerol  was  the  same  in  each  case. 


8?6.'- 

%."• 

Strips. 
A  B. 

Stripe, 
A  B. 

a 

(5040) 
1  5020  J 

.... 

5000(u-) 

88}—< 

b 

4910 

4880 

4850 

4860 

c 

4750 

4710 

4690 

4710 

d 

e 

f  One  I 

\  broad  \ 
{  band  j 

4560 
4440 

4520 
4360 

.... 

f 

4350 

4300 

4220 

g 

4220 

4160 

4100 

4090 

I 

4100 

4030 

3980 

3970 

i 

3970 

3900 

3890 

.... 

j 

.... 

3800 

3800 

( 

3700 

3690 

.... 

Plate  B  brings  out  clearly  the  fact  that  the  addition  of  water  causes 
the  uranyl  nitrate  bands  of  glycerol  to  be  gradually  shifted  towards  the 
violet.  The  above  identification  of  the  acetone  and  methyl  alcohol  bands 
is  open  to  correction. 

URANYL  NITRATE,  TEMPERATURE  EFFECT. 

A  spectrogram  was  made  of  a  0.0156  normal  uranyl  nitrate  solution  in 
water,  the  depth  of  layer  being  196  mm.  Exposures  were  made  to  the  Nernst 
glower  for  30  seconds,  the  current  being  0.8  ampere  and  the  slit-width 
0.20  mm.  The  length  of  exposure  to  the  spark  was  4  minutes.  Starting 
with  the  strip  nearest  the  scale,  the  temperatures  were  9°,  23°,  46°,  59°,  70°, 
and  79°. 

At  9°  the  ultra-violet  absorption  band  extended  to  A  3430.  Throughout 
the  blue-violet  band  there  was  considerable  transmission  at  this  temperature, 
the  stronger  spark  lines  being  only  partially  absorbed.  The  a,  b,  and  c  bands 
appeared,  all  being  extremely  weak,  however,  and  in  quite  striking  contrast 
with  their  strength  in  the  aqueous  solutions  investigated  in  the  earlier  part 
of  the  work.  Their  wave-lengths  were  >U  4550,  4705,  and  4870. 

As  the  temperature  was  raised,  both  the  ultra-violet  and  the  blue- 
violet  bands  widened.  The  intensity  of  the  uranyl  bands,  on  the  other 
hand,  did  not  seem  to  vary  with  the  temperature.  At  79°  the  ultra-violet 
band  extends  to  A  3550.  The  blue-violet  band  extends  from  A  3900  to  A  4450. 
Only  the  a  and  6  bands  appear  at  this  temperature,  their  positions  being 
A  4710  and  A  4875.  There  may  be  a  slight  shift  towards  the  red,  but  if 
there  is,  it  is  too  small  in  amount  to  be  established  with  certainty. 


URANIUM   SALTS.  107 

Plate  71,  A,  represents  the  effect  of  rise  in  temperature  on  the  absorp- 
tion spectra  of  a  ^  normal  solution  of  uranyl  nitrate.  From  the  fact  that 
the  uranyl  nitrate  bands  have  a  shorter  wave-length  than  the  bands  of  the 
other  salts,  it  was  thought  that  the  effect  of  temperature  might  be  different; 
that  at  high  temperatures  all  the  bands  might  have  the  same  positions. 
The  uranyl  nitrate  bands  shift  very  little  to  the  red,  if  they  shift  at  all,  for 
changes  in  temperature  of  90°.  The  effect  of  temperature  seems  to  be 
independent  of  the  temperature. 

ABSORPTION  SPECTRUM  OP  ANHYDROUS  URANYL  NITRATE. 

When  it  was  first  discovered  that  the  uranyl  nitrate  "  water  "  bands  were 
all  shifted  to  the  violet  with  reference  to  the  band  of  the  other  uranyl  salts  in 
water,  as  well  as  with  reference  to  the  uranyl  nitrate  bands  in  other  solvents, 
it  was  thought  that  possibly  it  was  more  hydrated  than  the  other  salts  in 
solution.  The  uranyl  salts  crystallized  from  aqueous  solutions  at  ordinary 
temperatures  have  the  following  composition:  UO2(N03)2.6H20,  UO2S04- 
3H2O,  U02(CH,COO)2.2H20,  and  UO2C12.H2O.  This  fact  would  favor  the 
supposition  that  in  solution  the  nitrate  might  be  more  hydrated  than  the 
other  salts.  The  fact  that  the  absorption  of  the  aqueous  solution  of  the 
nitrate  and  the  crystallized  salt  was  very  much  the  same,  as  far  as  the  posi- 
tions of  the  uranyl  bands  is  concerned,  also  seemed  to  favor  this  view. 

In  this  connection  it  was  considered  important  to  examine  the  absorp- 
tion spectrum  of  the  anhydrous  uranyl  nitrate.  This  salt  was  powdered 
and  placed  in  a  closed  glass  tube  just  above  the  slit  of  the  spectroscope. 
The  light  of  a  Nernst  glower  was  then  focused  upon  the  surface  of  the  salt 
nearest  the  slit  and  an  exposure  of  about  3  hours  made.  In  this  way  we 
examine  light  that  has  penetrated  a  short  distance  into  the  powder  and  is 
then  diffusely  reflected. 

The  absorption  spectrum  was  found  to  consist  of  quite  a  large  number 
of  bands  that  seem  quite  different  in  many  respects  from  those  of  the  solu- 
tion. The  following  are  the  approximate  wave-lengths:  M  4800,  4650,  4500, 
4420,  4360,  4280,  4180  (broad),  4060  (broad),  3950  (broad),  3820  (broad), 
3700  (narrow),  and  3600  (narrow).  The  bands  marked  broad  are  from  50 
to  60  Angstrom  units  wide  and  the  narrow  bands  about  20  Angstrom  units. 
If  the  first  band  is  the  a  band,  then  the  bands  of  the  anhydrous  salt  are  to 
the  violet  side  of  the  corresponding  bands  of  the  crystals  and  of  the  solu- 
tion. If  it  is  the  6  band  the  opposite  is  the  case.  On  account  of  the  small- 
ness  of  the  intensity  of  the  bands  it  could  not  be  settled  whether  A  4800  is 
the  a  or  the  6  band.  Further  investigation  of  this  point  will  be  made. 

There  are  two  difficulties  in  the  above  theory,  difficulties  for  which  no 
explanation  has  thus  far  been  suggested.  In  the  work  on  the  effect  of  rise 
in  temperature  on  the  absorption  spectrum  it  was  found  that  the  uranyl 
nitrate  bands  did  not  shift  to  the  red.  On  the  other  hand,  the  uranyl 
sulphate  and  uranyl  chloride  bands  were  shifted  to  the  red  under  the  same 
conditions.  (In  these  cases  aqueous  solutions  were  investigated.)  If  the 
uranyl  nitrate  bands  owe  their  position  to  a  large  amount  of  hydration,  it 
would  be  expected  that  with  rise  in  temperature  they  would  be  shifted 
towards  the  red  more  than  the  bands  of  the  sulphate  and  chloride.  Another 


108  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

difficulty  is  that  of  the  effect  of  dilution.  The  greater  the  dilution  the 
greater  the  dissociation,  and,  therefore,  according  to  the  theory  of  Arrhen- 
ius,  for  very  dilute  solutions  the  UO2  group  should  exist  in  the  ionic  condi- 
tion and  the  absorption  spectrum  of  all  the  salts  should  be  the  same,  i.  e., 
the  uranyl  bands  should  then  occupy  the  same  positions  independently  of 
the  kind  of  salt.  No  effect  of  this  kind  is  to  be  noticed,  as  was  shown  above 
under  the  division  describing  the  effect  of  dilution.  It  is  intended  to  use 
much  more  dilute  solutions  in  the  future. 

URANYL  BROMIDE  IN  WATER. 

In  Plate  72,  B,  we  have  the  absorption  spectra  of  uranyl  bromide 
(crystalline  salt,  U02Br2.H2O).  The  exposures  were  1  minute  to  the  Nernst 
glower  with  0.8  ampere  and  a  slit-width  of  0.08  mm.,  and  a  3-minute  expo- 
sure to  the  spark.  The  depth  of  the  cell  was  3  mm.  and  the  concentrations 
were  1,  0.75,  0.5,  0.33,  0.25,  0.2,  and  0.16  normal,  the  spectrum  for  the  most 
concentrated  solution  being  that  next  to  the  comparison  spectrum. 

It  will  be  seen  that  uranyl  bromide  gives  rise  to  an  absorption  very  simi- 
lar to  uranyl  nitrate,  there  being  a  blue-violet  and  an  ultra-violet  band.  The 
absorption  for  the  1  normal  solution  is  complete  for  all  wave-lengths  less  than 
X  4470.  For  0.75  normal  the  limits  of  the  blue-violet  band  are  U  4450  and 
3900,  the  ultra-violet  band  beginning  at  X  3800.  For  0.5  normal  the  blue- 
violet  band  shows  considerably  larger  transmission,  having  almost  com- 
pletely faded  out.  Its  middle  comes  at  about  A  4250.  The  ultra-violet  band 
gradually  recedes  towards  the  shorter  wave-lengths  as  the  dilution  increases. 

The  uranyl  bands  themselves  do  not  show  nearly  so  prominently  as 
in  the  case  of  the  chloride  and  nitrate.  The  bands  are  very  wide  and  diffuse. 
Their  approximate  positions  are:  a,  4880;  6,  4720;  c,  4560;  d,  4450;  e, 
4280;  /,  4160. 

The  spectrogram  showing  a  series  to  test  Beer's  law  is  given  in  Plate 
72,  A.  The  concentrations,  beginning  with  the  strip  nearest  the  num- 
bered scale,  are  1,  0.75,  0.5,  0.33,  0.25,  0.2,  and  0.16  normal,  the  correspond- 
ing depths  of  cell  being  3,  4,  6,  9,  12,  18,  and  24  mm.,  respectively.  Beer's 
law  is  found  to  hold,  the  limits  of  the  absorption  bands  being  independent 
of  the  above  range  of  concentrations.  The  ultra-violet  band  and  blue- violet 
band  have  a  small  region  of  transmission  between  them  which  shows  in  the 
original  film  but  not  on  the  print  from  it.  This  region  of  transmission  is 
very  faint  and  is  quite  a  sensitive  index  to  any  possible  deviations  from 
Beer's  law.  It  shows  no  changes  in  intensity  with  change  in  concentration. 
The  uranyl  bands  a  and  b  show,  although  they  are  very  indefinite.  Concen- 
tration does  not  affect  their  intensity  in  the  least  as  far  as  can  be  detected. 

URANYL  SULPHATE,  TEMPERATURE  EFFECT. 

A  spectrogram  (Plate  73,  A)  was  made  for  a  normal  solution  of  uranyl 
sulphate,  the  depth  of  cell  being  3  mm.  The  time  of  exposure  was  90  seconds 
to  the  Nernst  glower  with  a  current  of  0.8  ampere  and  a  slit-width  of  0.20 
mm.  The  time  of  exposure  to  the  spark  was  6  minutes.  Starting  with  the 
strip  nearest  to  the  numbered  scale,  the  temperatures  were  5°,  19°,  32°,  54°, 
67°,  and  84°. 


URANIUM   SALTS.  109 

The  rise  in  temperature  from  5°  to  84°  caused  an  encroachment  of  the 
ultra-violet  band  into  the  regions  of  greater  wave-length.  The  blue-violet 
band  increased  in  width,  especially  towards  the  red,  as  the  temperature  was 
raised.  The  uranyl  bands  themselves  changed  very  slightly  in  intensity 
with  rise  in  temperature. 

At  5°  the  ultra-violet  was  absorbed  to  >l  3500.  The  blue-violet  band 
extended  from  A  3900  to  A  4400.  The  uranyl  bands  a,  b,  and  c  appeared  at 
U  4570,  4730,  and  4910. 

At  84°  the  ultra-violet  band  extended  to  A  3600,  the  blue-violet 
band  from  A  3850  to  A  4550.  The  bands  a,  6,  and  c  have  become  con- 
siderably more  diffuse.  Their  positions  are  >U  4590,  4745,  and  4925, 
approximately. 

A  much  more  dilute  solution  (0.0156  normal)  of  uranyl  sulphate 
(Plate  73,  B),  containing  approximately  the  same  amount  of  salt  as  the 
concentrated  solution,  was  used.  The  length  of  cell  in  this  case  was  196 
mm.  The  exposure  was  for  30  seconds  to  the  Nernst  glower  (current  0.8 
ampere,  slit-width  0.20  mm.).  The  time  of  exposure  to  the  spark  was  4 
minutes.  Starting  with  the  strip  next  to  the  comparison  spectrum,  the 
temperatures  were  6°,  19°,  36°,  51°,  67°,  and  81°. 

At  6°  the  ultra-violet  band  extends  to  A  3500  and  the  blue-violet 
band  from  X  3950  to  A  4450.  The  positions  of  the  a,  b,  and  c  bands  are 
M  4565,  4720,  and  4895.  At  81°  the  ultra-violet  absorption  extended  to 
A  3600  and  the  blue-violet  band  from  X  3900  to  /I  4500.  The  a  and  6  bands 
were  located  at  >U  4735  and  4915.  The  effect  of  concentration  on  the 
temperature  coefficient  seems  to  be  very  small.  In  both  concentrations, 
as  the  temperature  was  raised  there  was  a  slight  shift  of  the  uranyl  bands 
to  the  red. 

Several  spectrograms  were  made  in  order  to  get  the  absorption  spectra 
of  the  dry  (anhydrous)  uranyl  sulphate.  The  bands  were  extremely  faint, 
however,  and  no  reliable  measurements  of  their  position  could  be  made. 

UEANYL  SULPHATE  MIXED  WITH  CONCENTRATED  SULPHUBIC  ACID. 

Several  spectrograms  were  taken  to  find  whether  the  addition  of  very 
concentrated  sulphuric  acid  to  an  aqueous  solution  of  uranyl  sulphate  pro- 
duced any  effect.  A  normal  solution  was  used — a  spectrogram  being  taken  of 
this  solution.  Very  concentrated  sulphuric  acid  was  added  until  the  length 
of  the  layer  was  57.6  mm.;  the  concentration  being  then  0.052  normal. 
In  both  spectrograms  the  position  of  the  long  wave-length  side  of  the  blue- 
violet  band  remained  the  same.  The  bands  a  and  6  appear  in  both  cases, 
and  c  rather  faintly.  In  the  aqueous  solution  6  is  about  five  times  stronger 
than  a.  In  the  sulphuric  acid  mixture,  however,  a  increases  in  intensity; 
i.e.,  its  absorption  becomes  greater;  whereas  b  becomes  considerably  nar- 
rower, so  that  a  and  6  have  about  the  same  intensity.  The  uranyl  sulphate 
bands  in  the  sulphuric  acid  solution  resemble  very  closely  the  same  bands 
for  uranyl  nitrate  crystals. 

In  very  strong  sulphuric  acid  the  bands  of  uranyl  sulphate  have 
the  following  wave-lengths:  a,  A  4930,  about  30  Angstrom  units  wide; 
b,  X  4745,  almost  identical  in  character  with  o;  c,  A  4550,  about  80  Ang- 


110  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

strom  units  wide  and  appears  sometimes  to  be  double;  d,  I  4380  (70  Ang- 
strom units);  e,  A  4240  (70  Angstrom  units  wide);  /,  A  4100;  g,  *  3980; 
h,  I  3870;  i,  X  3770;  /,  X  3660. 

URANYL  ACETATE  IN  WATER. 

Uranyl  acetate  crystallizes  from  an  aqueous  solution  at  ordinary  tem- 
peratures as  UC^CI^COO^HjjO.  The  aqueous  solution  of  this  salt  is 
very  similar  to  that  of  the  uranyl  salts  previously  described,  showing  the 
blue-violet  and  ultra-violet  bands  and  also  the  characteristic  uranyl  bands. 
This  salt  in  solution  is  much  more  highly  colored  for  the  same  concentra- 
tion than  the  nitrate  or  bromide. 

Plate  74,  B,  represents  the  absorption  of  a  series  of  solutions  where 
the  concentration  was  kept  constant  and  the  depth  of  layer  varied.  The 
usual  procedure  was  to  keep  the  concentration  constant  and  vary  the  depth 
of  cell.  For  salts  obeying  Beer's  law  this  would  give  the  same  absorption 
as  keeping  the  depth  of  cell  constant  and  varying  the  concentration,  so  that 
in  our  spectrograms  of  a  salt  where  Beer's  law  holds  no  difference  is  made 
between  these  two  cases.  Where  Beer's  law  is  deviated  from,  the  two  cases 
will  not  be  identical.  For  the  case  under  consideration  the  concentration 
was  0.031  normal  and  the  depths  of  cell,  starting  with  the  strip  nearest  the 
numbered  scale,  were  24,  18,  12,  9,  6,  4,  and  3  mm.  The  length  of  exposure 
to  the  Nernst  glower  with  0.08  ampere  and  a  slit-width  of  0.08  mm.  was 
1  minute. 

The  blue-violet  band  has  the  boundaries  AA  4500  and  4050  for  a  24  mm. 
cell,  and  AA  4400  and  4100  for  a  depth  of  18  mm.,  the  middle  of  the  band 
thus  coming  at  about  A  4250.  The  long  wave-length  edges  of  the  ultra- 
violet band  are  AA  3750,  3700,  3680,  3660,  3630,  3600,  and  3580  for  depths 
of  cell  of  24,  18,  12,  9,  6,  4,  and  3  mm.,  respectively. 

A  photograph  was  made  to  bring  out  the  small  uranyl  bands.  An 
exposure  was  first  made  for  1  minute  (0.08  ampere  and  0.08  mm.  slit)  in 
the  yellow  end  of  the  spectrum.  This  solution  was  15  mm.  deep  in  every 
case.  The  screen  was  interposed  so  as  to  cut  off  all  light  of  greater  wave- 
length than  A  4450.  A  long  exposure  to  the  Nernst  filament — about  5 
minutes — was  then  made.  Another  screen  was  then  interposed  which  cut 
out  all  light  of  wave-length  greater  than  A  2800,  and  an  exposure  made  to 
the  spark.  During  these  three  exposures  nothing  was  moved  except  the 
screen,  and  thus  the  question  of  any  mechanical  moving  of  the  photographic 
film  was  eliminated.  From  these  two  plates  the  positions  of  9  uranyl  bands 
were  measured.  These  were  as  follows:  a,  4910(?);  6,  4740;  c,  4595;  d, 
4455(7);  e,  4310;/,  4160;  g,  4070;  h,  3970;  i,  3865. 

It  will  be  seen  that  these  bands  are  all  nearer  the  red  than  the  bands 
of  uranyl  nitrate  in  water. 

Deussen  found  the  following  values:  a,  4875;  6,  4730;  c,  4575;  d,  4420; 
e,  4310; /,  4180;  g,  4060;  h,  3950;  i,  3860;  j,  3770.  These  are  in  satisfactory 
agreement  with  the  values  given  above. 

The  spectrogram,  Plate  74,  A,  represents  the  change  in  absorption  of 
uranyl  acetate  with  concentration  when  the  amount  of  salt  in  the  path  of 
the  light  beam  is  kept  constant.  The  exposure  was  1  minute  to  the  Nernst 


URANIUM   SALTS.  Ill 

glower,  with  0.8  ampere  (slit  0.08  mm.) ,  and  3  minutes  to  the  spark.  Starting 
from  the  comparison  spectrum  the  concentrations  are  0.25,  0.185,  0.125, 
0.083,  0.0625,  0.042,  and  0.031  normal,  the  corresponding  depths  of  cell 
being  3,  4,  6,  9,  12,  18,  and  24  mm. 

This  uranyl  salt  shows  a  deviation  from  Beer's  law  which  is  different 
from  the  deviation  of  any  salt  previously  studied.  All  other  salts  show,  for 
a  Beer's  law  series,  a  greater  absorption  at  the  greater  concentration. 
Uranyl  acetate  shows  the  opposite,  a  greater  absorption  for  the  less  concen- 
trated solutions.  For  the  0.25  normal  solution  the  blue-violet  band  extends 
from  A  4150  to  A  4250.  At  0.031  normal  it  has  broadened,  so  that  its  limits 
are  AA  4500  and  4050.  This  broadening  of  the  absorption  is  gradual.  In 
like  manner  the  ultra-violet  band  extends  to  A  4400  for  the  0.25  normal 
solution  and  to  A  4300  for  the  0.031  normal  solution. 

A  0.188  normal  solution  of  uranyl  acetate  14  mm.  in  length  was  diluted 
to  0.007  normal  and  380  mm.  in  length.  The  absorption  was  found  to  be 
greater  for  the  more  dilute  solution.  The  uranyl  bands  were  not  shifted 
and  were  much  broader  in  the  dilute  solution. 

ANHYDROUS  URANYL  ACETATE. 

To  determine  whether  the  water  of  crystallization  of  uranyl  acetate, 
U02(CH3COO)2.2H20,  had  any  effect  on  the  position  of  the  uranyl  acetate 
bands,  the  absorption  of  the  anhydrous  salt  was  found  in  the  same  way  as 
for  uranyl  nitrate.  Seven  bands  could  be  detected,  but  most  of  them  were 
quite  faint,  although  stronger  than  the  bands  of  the  nitrate:  a,  4905;  6, 
4775;  c,  4605;  d,  4460;  e,  4320;  /,  4200;  g,  4085.  It  will  be  seen  that  there 
is  a  slight  shift  towards  the  red  as  compared  with  the  aqueous  solution. 

URANYL  ACETATE  IN  METHYL  ALCOHOL. 

For  the  uranyl  acetate  the  exposure  to  the  Nernst  glower,  with  0.8 
ampere  and  a  slit-width  of  0.08  mm.,  was  1  minute.  No  exposure  was 
made  to  the  spark  except  for  a  comparison  spectrum.  Starting  with  the 
strip  nearest  the  spark  scale,  in  Plate  75,  B,  the  concentrations  were  0.25, 
0.20,  0.16,  0.12,  0.10,  0.07,  and  0.06  normal.  The  depth  of  cell  was  constant, 
6mm.  The  edges  of  the  blue-violet  absorption  were  as  follows:  0.25  nor- 
mal, AA  4550  and  3850,  0.20  normal,  AA  4520  and  3900,  0.16  normal  AA  4500 
and  3950,  and  0.12  normal  AA  4550  and  4000.  The  middle  of  the  band  would 
thus  come  at  about  A  4270.  As  the  spark  was  not  used  the  exact  edges  of 
the  ultra-violet  band  can  not  be  given. 

The  uranyl  bands  had  the  following  positions:  a,  4875;  b,  4720;  c, 
4585;  d,  4445;  e,  4320;  /,  4185;  g,  4070;  h,  3975. 

A  plate  was  made  to  test  Beer's  law.  Starting  with  the  strip  nearest 
the  comparison  scale  the  concentrations  were  0.25,  0.20,  0.16,  0.12,  0.10, 
0.07,  and  0.06  normal,  the  corresponding  depths  of  cell  being  6,  7.5,  9.5,  12, 
15,  19,  and  24  mm.  The  deviation  from  Beer's  law  is  the  same  in  direction 
as  for  uranyl  acetate  in  aqueous  solution  and  is  not  nearly  so  great.  For 
the  0.25  normal  solution  the  limits  of  the  blue-violet  band  were  AA  4470  and 
3925,  the  distance  between  the  blue-violet  band  and  the  ultra-violet  band 


112 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 


at  this  concentration  being  about  100  Angstrom  units.  For  the  0.06 
normal  solution  the  blue-violet  and  ultra-violet  bands  have  completely 
merged  and  the  limit  of  absorption  is  about  A  4600. 

THE  URANYL  BANDS  OP  THE  ACETATE. 

The  following  table  gives  the  approximate  wave-lengths  of  the  uranyl 
bands  of  the  acetate  in  water  and  in  methyl  alcohol,  and  of  the  anhydrous 
powder: 

Bands  of  uranyl  acetate. 


a. 

b. 

c. 

d. 

«. 

/. 

0. 

h. 

i. 

Water  

4910 

4740 

4595 

4455 

4310 

4160 

4070 

3970 

3830 

Methyl  alcohol  
Anhydrous  salt  

4880 
4910 

4720 
4780 

4590 
4610 

4450 
4460 

4320 
4320 

4190 
4200 

4070 
4090 

3980 

From  this  table  it  seems  that  the  positions  of  the  bands  of  the  acetate 
under  these  different  conditions  are  about  the  same. 

URANYL  ACETATE,  TEMPERATURE  EFFECT. 

A  spectrogram  showing  the  effect  of  rise  in  temperature  was  made  for 
a  0.0039  normal  aqueous  solution  of  uranyl  acetate  196  mm.  deep.  The 
exposures  were  made  for  30  seconds  to  the  Nernst  glower,  with  a  current 
of  0.8  ampere  and  a  slit-width  of  0.20  mm.  No  exposure  was  made  to  the 
spark  at  all.  The  temperatures,  starting  with  the  strip  nearest  the  com- 
parison spectrum,  were  6°,  18°,  30°,  43°,  56°,  68°,  and  75°. 

The  spectrogram  shows  the  ultra-violet  and  blue -violet  bands  common 
to  all  uranyl  salts.  The  transmission  band  between  these  absorption  bands 
is  about  200  Angstrom  units  wide  and  changes  very  little  with  change  in 
temperature.  The  blue-violet  band  advances  rapidly  towards  the  red  as 
the  temperature  rises.  At  6°  the  blue-violet  band  extends  from  X  3950 
to  A  4500.  The  latter  edge  gradually  runs  towards  the  red  until  at  75°  it 
is  about  X  4600.  The  uranyl  bands  a  and  b  appear.  They  are  very  weak 
and  gradually  shift  towards  the  red  with  rise  in  temperature. 

SPECTROPHOTOGRAPHY  OF  CHEMICAL  REACTIONS  OF  URANYL  SALTS. 

Plate  81,  B}  represents  the  absorption  spectrum  of  a  solution  15  mm.  in 
depth  and  containing  an  0.08  normal  solution  of  a  uranyl  salt  in  water. 
Beginning  with  an  0.08  normal  solution  of  uranyl  nitrate,  sulphuric  acid 
was  added  so  as  to  make  the  concentration  of  acid  beginning  with  strip  1 
as  follows:  0.37,  0.73,  1.46,  2.92,  5.84,  10.22,  and  14.60  normal. 

It  will  be  seen  that  in  strip  1  we  have  practically  the  sulphate  spectrum, 
most  of  the  nitrate  having  been  transformed.  The  addition  of  more  acid 
does  not  produce  any  marked  change  until  we  reach  the  sixth  and  seventh 
strips.  Here  we  see  that  the  c  and  d  bands  are  very  greatly  shifted,  so  that 
in  the  latter  strip  they  form  a  single  band.  Several  of  the  other  bands  are 
considerably  shifted  towards  the  red.  Throughout  the  changes  of  conditions 
above  named,  the  bands  remain  quite  sharp  and  well  defined  (for  uranyl 
bands),  and  change  very  little  in  intensity.  This  is  in  quite  marked 


URANIUM   SALTS. 


113 


contrast  with  many  of  the  plates  in  which  there  are  certain  stages  that 
hardly  show  any  uranyl  bands  at  all,  whereas  at  other  stages  the  bands 
will  be  very  strong  indeed. 

The  bands  in  the  upper  strips  beyond  the  region  ^  5000  are  probably 
due  to  nitric  oxide.    Several  of  the  bands  are  quite  strong. 


Nitrate 
bands. 

Sulphate 
bands. 

Strip  1. 

Strip  5. 

Strip  6. 

Strip  7. 

5230? 

5200? 

5170? 

5100? 

5000? 

a 

f4890 
14800 

}  4900 

4900  to  5100  j  4910 

4920 

4920 

b 

(4742 
\4722 

}  4740 

4730 

4750 

4740 

c 

4540 

4580 

4570 

4570 

4570  \ 

d 

4390 

4460  i  4440 

4450 

4480  J 

4550 

e 

4330  I  4320 

4340 

4340 

4370 

f 

iiss 

4200  i  4200 

4200 

4210 

4225 

g 

4030 

4070 

4070 

4070 

4080 

4090 

h 

3905 

3970 

3950 

3970 

3960 

3970 

i 

3815 

3850 

3850 

3850- 

3860 

3860 

1 

3710 

3740 

3720 

3740 

3750 

3760 

k 

3620 

3620 

3640 

3650 

I 

35i5 

3530 

3520 

3520 

The  simplest  interpretation  of  this  plate  is  that  as  more  and  more 
sulphuric  acid  is  added  molecules  are  formed  that  contain  more  and  more 
of  the  acid.  That  there  are  several  of  these  compounds  formed  seems 
probable,  since  the  shift  of  the  bands  is  quite  large  and  this  shift  takes 
place  gradually. 


Nitrate 
bands. 

Chloride 
bands. 

Strip  1. 

Strip  6. 

Strip  7. 

a 

f4890> 
I  4800  I 

4920 

b 

(  47421 
14722/ 

4740 

4700  weak  and  broad 

4720 

4740 

c 

4540 

4560 

4560  weak  and  broad 

4580 

4580 

d 

4390 

4460 

44  10  weak  and  broad        4430 

4440 

e 

4315 

4270  strong 

4280 

f 

4155 

4170 

4  140  strong 

4145 

9 

4030 

4025 

4020  strong 

4020 

h 

3905 

.... 

3900 

3900 

3900 

i 

3815 

3800 

3800 

i 

3710 

3700 

3700 

3700  weak 

k 

3600 

3600 

3600  weak 

I 

35is 

3500 

3500 

Plate  83,  A,  gives  the  effect  of  adding  sulphuric  acid  to  an  aqueous 
solution  of  uranyl  nitrate.  The  first  strip  here  gives  the  absorption  of 
uranyl  nitrate  to  which  no  acid  has  been  added.  The  changes  here  are 

8 


114 


A    STUDY   OF   THE   ABSORPTION    SPECTRA. 


from  the  neutral  nitrate  bands  to  the  neutral  sulphate  bands,  approxi- 
mately. There  is  in  this  case  a  gradual  shift  of  the  bands  to  the  red. 

Plate  79,  B,  represents  the  effect  of  adding  hydrochloric  acid  to  an 
aqueous  solution  of  uranyl  nitrate.  The  depth  of  cell  was  15  mm.  The 
concentration  of  the  uranyl  salt  was  kept  constant.  The  percentages  of 
acid  were  increased. 

In  the  first  strips  the  b  and  c  bands  are  very  weak.  They  become 
stronger  and  shift  gradually  to  the  red.  The  other  bands  are  quite  sharp 
until  the  last  strip,  where  they  appear  very  weak.  Their  wave-lengths  are 
but  slightly  changed.  In  the  above  table  the  wave-lengths  of  the  neutral 
chloride  and  nitrate  bands  are  taken  from  the  other  tables.  Strip  1  of  this 
plate  and  strip  1  of  Plate  81,  B,  are  entirely  different. 

Plate  83,  B,  represents  the  absorption  spectra  of  uranyl  nitrate  to 
which  acetic  acid  had  been  added.  Plate  82,  A,  represents  the  same  effect, 
except  that  here  the  original  uranyl  nitrate  solution  was  only  1  mm.  in 
thickness;  so  that  the  ratio  of  acetic  acid  to  the  amount  of  uranyl  salt  was 
much  larger. 


Uranyl 
nitrate. 

Strip  1. 
Plate  83.  B. 

Strip  6. 
Plate  83.  B. 

Strip  1. 
Plate  82.  A 

Strip  3. 
Plate  82.  A. 

Strip  5. 
Plate  82,  A. 

Uranyl 
acetate. 

a 

{4890} 

4830? 

b 

14722/ 

4660 

4675 

4860 

4900 

e 

4540 

4510 

4520 

4650 

4720 

4770 

d 

4390 

4370 

4380 

4420  weak 

4500 

4570 

4600 

e 

.... 

4245 

4250 

4270 

4350 

4440 

4460 

f 

4155 

4130 

4140 

4150 

4220 

/4340 
14220 

4320 
4200 

g 

4030 

4020 

4030 

4020 

4030 

4120 

4090 

I 

3905 

3910 

3920 

3910 

3910 

4010 

3975 

i 

3815 

3800 

3810 

3800 

3870 

3710 

3670 

3700 

3700 

3770 

3570 

3580 

3600 

3670 

I 

35i5 

3460 

3460 

The  first  effect  which  the  addition  of  acetic  acid  produces  is  to  shift 
slightly  the  uranyl  bands  of  the  nitrate  to  the  red,  and  to  cause  them  to 
become  much  sharper.  When  some  twenty  times  as  much  strong  glacial 
acetic  acid  had  been  added  as  was  equivalent  to  the  uranyl  nitrate  solu- 
tion, the  uranyl  bands  became  quite  weak,  and  shifted  very  greatly 
towards  the  red,  as  is  shown  in  Plate  82,  A.  The  e  and  /  bands  are  each 
shifted  nearly  200  Angstrom  units.  When  this  enormous  shift  towards 
the  red  takes  place  a  new  band  appears  between  /and  g.  This  new  band 
will  be  called/,.  Further  addition  of  acetic  acid  causes  the  uranyl  bands 
to  become  stronger  again,  producing  at  the  same  time  a  small  shift  to 
the  red. 


URANIUM    SALTS. 


115 


URANYL  CHLORIDE  IN  WATER,  CONDUCTIVITY  AND  TEMPERATURE  COEFFICIENTS. 

Uranyl  chloride,  like  other  uranyl  salts,  is  strongly  hydrolyzed  in  dilute 
solution. 


Temperature  coefficients. 

36° 

60° 

V. 

35°  to  50°. 

50°  to  66°. 

Mt> 

Mt> 

MV 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

220.4 

274.6 

333.2 

3.61 

.64 

3.91 

1.42 

8 

253.5 

318.9 

387.8 

4.36 

.72 

4.59 

1.44 

32 

301.4 

380.3 

473.2 

5.26 

.74 

6.19 

1.63 

128 

342.0 

439.4 

548.5 

6.49 

.90 

7.27 

1.65 

512 

379.4 

491.1 

610.6 

7.45 

.96 

7.97 

1.62 

"  -48 

418.5 

546.8 

693.7 

8.55 

2.04 

9.79 

1.97 

URANYL  NITRATE  IN  WATER,  CONDUCTIVITY  AND  TEMPERATURE  COEFFICIENTS. 
The  salts  of  uranium,  like  the  salts  of  chromium,  undergo  hydrolysis 
at  the  higher  dilutions,  and  the  dissociations,  therefore,  can  not  be  cal- 
culated. 


Temperature  coefficients. 

V. 

36°  to  50°. 

60°  to  66°. 

M« 

M 

Mt> 

Cond. 
units. 

Per  cent. 

Cond. 
units. 

Per  cent. 

4 

176.0 

220.1 

268.3 

2.94 

1.67 

2.21 

.46 

8 

199.2 

251.2 

307.1 

3.46 

1.74 

3.73 

.48 

32 

233.8 

298.0 

372.0 

4.28 

1.83 

4.93 

.65 

128 

275.4 

354.6 

444.7 

5.28 

1.92 

6.01 

.69 

512 

303.2 

395.8 

502.0 

6.17 

2.03 

7.08 

.79 

2048 

349.0 

460.8 

585.3 

7.45 

2.13 

8.30 

.80 

URANYL  SULPHATE  IN  WATER,  CONDUCTIVITY  AND  TEMPERATURE  COEFFICIENTS. 

The   temperature   coefficients  in   per  cent,    as  with   uranyl  acetate, 
decrease  with  increase  in  dilution. 


Temperature  coefficients. 

V. 

35°  to  60°. 

60°  to  65°. 

Mt» 

M» 

M» 

Cond. 
units. 

Percent. 

Cond. 
units. 

Per  cent. 

16 

90.10 

110.5 

131.3 

1.36 

1.51 

1.39 

1.26 

32 

115.9 

139.5 

162.8 

1.57 

1.35 

1.55 

1.11 

128 

155.0 

185.0 

213.7 

2.00 

1.29 

1.91 

1.03 

512 

219.0 

264.3 

303.7 

3.02 

1.38 

2.63 

0.99 

116 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


UBANYL  ACETATE  IN  WATER,  CONDUCTIVITY  AND  TEMPERATURE  COEFFICIENTS. 
It  will  be  seen  that  the  temperature  coefficients  expressed  in  per  cent 
decrease  with  increase  in  the  dilution.    This  is  rather  unusual;  these  coeffi- 
cients, as  a  rule,  increasing  with  the  dilution. 


65° 

Temperature  coefficients. 

V. 

35°  to  50°. 

CO0  to  65°. 

P9 

MV 

M« 

Cond. 
unita. 

Per  cent. 

Cond. 
units. 

Per  cent. 

16 

48.06 

59.34 

71.36 

0.75 

.56 

0.80 

1.34 

32 

54.92 

67.36 

80.47 

0.83 

.51 

0.87 

1.29 

128 

72.26 

87.65 

103.40 

1.02 

.41 

1.05 

1.19 

512 

92.92 

111.30 

130.00 

1.22 

.31 

1.25 

1.12 

2048 

118.40 

141.40 

165.40 

1.53 

.29 

1.60 

1.13 

THE  PHOSPHORESCENT  AND  FLUORESCENT  SPECTRA  OF  URANYL  SALTS. 

Many  bodies  on  being  exposed  to  light,  X-rays,  a,  /?,  7-,  or  cathode  rays, 
on  being  heated  or  rubbed,  emit  light.  This  is  generally  called  phospho- 
rescence when  the  light  is  emitted  after  the  stimulating  agent  ceases  to  act, 
and  fluorescence  when  the  excited  light  ceases  to  be  emitted  as  soon  as  the 
exciting  cause  ceases.  In  general,  liquids  and  gases  fluoresce  while  solids 
phosphoresce.  Some  of  the  strongest  phosphorescent  compounds  are  the 
uranyl  salts.  These  salts  emit  bands  of  phosphorescent  light  in  the  green 
region  of  the  spectrum. 

The  researches  of  Lecocq  de  Boisbaudran,  Lenard  and  Klatt,  Urbain, 
and  others,  upon  the  rare  earths,  the  sulphur  compounds  of  the  alkaline 
earths,  and  the  oxides  of  the  earth  metals,  have  shown  that  these  substances 
do  not  phosphoresce  when  in  the  pure  state,  and  that  the  presence  of  an 
impurity  seems  to  be  essential  to  the  formation  in  those  substances  of  the 
complex  molecules  or  "  centra"  that  emit  the  phosphorescent  light.  On  the 
other  hand,  the  uranyl  salts  always  phosphoresce. 

Lenard  and  Klatt  *  have  investigated  very  thoroughly  various  cal- 
cium phosphates  of  bismuth,  manganese,  and  nickel.  At  ordinary  tem- 
peratures the  bands  are  very  broad,  ill-defined,  and  are  unaffected  by  a 
magnetic  field.  Lenard  and  Klatt  believe  that  there  are  certain  places 
in  atoms  that  can  store  electrons.  These  dynamids  are  only  supposed  to 
hold  the  electrons  at  low  temperatures.  At  high  temperatures  the  electrons 
possess  a  much  greater  freedom  of  motion.  The  different  states  of  motion 
are  visualized  as  three  kinds:  the  "gaseous,"  "liquid,"  and  "solid"  states. 
In  the  "gaseous  "  state  the  electrons  can  occasion  the  conduction  of  elec- 
tricity between  the  atoms  if  the  latter  exist  in  the  same  way  as  they  do  in 
metals.  In  the  "liquid  "  state  the  electrons  are  in  a  state  of  motion  sensi- 
tive to  light  vibrations  and,  hence,  they  take  part  in  light  absorption.  In 
the  "  solid  "  state  the  electrons  take  part  neither  in  conduction  nor  in 


Ann.  Phys.,  15,  225,  451,  633  (1904). 


URANIUM   SALTS.  117 

absorption.  At  low  temperatures  the  spheres  of  influence  of  the  dynamids 
are  considered  to  extend  to  greater  distances  than  at  high  temperatures, 
and  the  free  paths  of  the  electrons  are  also  greatly  reduced. 

To  each  phosphorescent  band  Lenard  and  Klatt  assign  three  phases: 
An  upper  momentary  or  heat  phase;  a  permanent  phase  possessing  quite 
definite  temperature  limits;  and  a  lower  momentary  or  cold  phase.  These 
phases  succeed  each  other  as  the  temperature  falls.  The  upper  momentary 
phase  results  when  the  dynamids  do  not  store  electrons.  Whenever  elec- 
trons are  stored,  these  return  afterwards  to  the  atom  from  which  they  were 
expelled  by  the  light-wave,  and  produce  the  permanent  phase  of  the  phos- 
phorescent band.  At  low  temperatures  a  few  electrons  return  to  the 
atoms  from  which  they  were  expelled  and  these  cause  the  lower  momentary 
phase. 

In  general  the  temperature  of  solid  hydrogen  is  sufficiently  low  to 
bring  all  phosphors  into  the  lower  momentary  phase.  Lowering  the  tem- 
perature to  — 180°  continually  causes  new  bands  to  appear  in  the  perma- 
nent phase.  Among  such  bands  of  long  duration,  for  example,  is  the  Ca.Ni/3 
band,  or  the  orange  afterglow  of  BaCu.  According  to  Lenard  and  Klatt 
uranyl  compounds  show  only  the  upper  momentary  phase. 

There  are  definite  wave-lengths  which  in  all  temperature  phases 
of  the  centra  bring  into  phosphorescence  only  the  momentary  phase. 
The  electrons  under  the  photoelectric  influence  of  these  wave-lengths  are 
ejected  from  the  metallic  atoms  of  the  centra,  and  then  return  almost 
immediately  to  the  metallic  atom  again;  thus  causing  the  emission  of 
light.  Other  wave-lengths  cause  the  electrons  to  be  ejected  from  the 
same  centra,  but  in  this  case  the  electrons  are  retained  in  the  neighbor- 
hood. These  stored  electrons,  when  they  finally  return  to  the  atom 
from  which  they  were  ejected,  produce  the  phosphorescent  band  of  the 
permanent  phase. 

The  phenomena  of  luminescence  are  generally  conceded  to  be  due  to 
some  kind  of  electrolytic  dissociation  or  ionization  of  the  dissolved  sub- 
stance in  the  medium  about  it.  Among  the  first  to  hold  this  view  were 
Wiedeman  and  Schmidt.1  The  theory  explains  Stokes'  law  2  and  most  of 
the  other  properties  of  phosphorescence.  Some  of  these  other  properties 
are  as  follows :  The  distribution  of  intensity  throughout  a  phosphorescent 
band  is  independent  of  the  intensity  and  the  wave-length  of  the  exciting 
light;  the  light  emitted  from  an  isotropic  medium  is  unpolarized;  during 
the  decay  of  phosphorescence  each  band  behaves  as  an  individual  unit; 
the  decay  curve  is  dependent  on  the  intensity  and  duration  of  excita- 
tion ;  the  behavior  of  a  phosphorescent  body  depends  upon  its  past  history. 

Wiedeman  and  Schmidt  have  suggested  that  some  of  the  ions  produced 
during  phosphorescent  excitation  form  semi-stable  combinations  with  the 
solvent  molecules,  and  that  after  excitation  these  combinations  are  broken 
down.  Merritt 3  further  discusses  the  theory  of  Wiedeman  and  Schmidt. 

'Ann.  Phys.,  56,  177  (1895). 
2  Phys.  Rev.,  22,  279  (1906) 
•  Ibid.,  27,  384  (1908). 


118  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

He  considers  that  the  first  effect  of  the  exciting  light  is  to  produce  dissoci- 
ation. This  dissociation  may  be  either  chemical  or  electrolytic.  Electro- 
lytic dissociation  may  consist  of  a  dissociation  similar  to  that  taking  place 
in  ordinary  electrolysis,  or  in  the  expulsion  of  one  or  more  electrons  from 
the  molecule.  Suppose  that  an  electron  is  expelled  from  the  atom;  the  two 
resulting  ions  will  then  have  very  different  mobilities.  The  electrons  will 
only  temporarily  attach  themselves  to  molecules  on  account  of  their  great 
velocities.  The  positive  ions,  on  the  other  hand,  will  much  more  likely 
attach  themselves  either  to  the  solvent  molecules  or  to  other  molecules  of 
the  active  substance.  For  the  reason  that  the  mobility  of  the  positive  ion 
is  small,  Merritt  considers  that  the  combinations  which  it  forms  are  much 
more  stable  than  those  formed  by  the  electrons. 

As  there  are  different  kinds  of  combinations  present  there  will  be 
different  kinds  of  collisions,  and  it  is  in  collisions  and  recombinations 
of  this  kind  that  one  is  to  find  the  source  of  the  light  emitted  during 
phosphorescence.  The  vibrations  corresponding  to  the  different  modes 
of  recombination  will  probably  differ  in  violence,  frequency,  and  radiating 
power. 

Very  important  work  has  been  done  by  Urbain1  and  others  upon  the 
phosphorescence  of  the  rare  earths.  To  each  one  of  the  elements  of  the  rare 
earths  there  corresponds  a  definite  atomic  weight,  definite  arc  and  spark 
spectra,  and  definite  absorption  and  phosphorescent  spectra.  The  oxides  of 
europium,  gadolinium,  terbium,  dysprosium,  etc.,  are  not  phosphorescent. 
Mixtures  of  these  compounds  are,  however,  extremely  phosphorescent, 
and  in  general  there  is  a  certain  proportion  at  which  the  phosphorescence  is 
a  maximum.  For  example,  one  part  of  the  oxide  of  europium  in  two 
hundred  and  fifty  parts  of  gadolinium  gives  a  maximum  europium  phos- 
phorescence. The  phosphorescence  in  this  case  is  due  to  the  europium 
atom  or  molecule,  and  is  not  greatly  affected  by  the  diluent.  However, 
different  diluents  as  lime  or  gadolinium  do  show  a  slight  effect  upon  the 
resulting  spectra.  The  temperature  of  calcination  and  the  acid  radical  of 
the  diluent  also  have  an  influence.  For  mixtures  of  europium  and  calcium 
compounds  there  exist  two  different  sets  of  bands  possessing  different 
optima.  Mixtures  of  europium  and  gadolinium,  calcined  at  1000°  C.  and 
1600°  C.,  give  entirely  different  phosphorescent  spectra.  Gadolinium  is 
much  more  effective  in  exciting  phosphorescence  than  calcium.  The  spec- 
tra of  different  diluents  do  not  change  into  each  other  but  remain  fixed, 
the  intensity  being  the  only  variable. 

A  considerable  amount  of  work  on  the  phosphorescence  of  uranyl  com- 
pounds has  been  done  by  the  Becquerels.  E.  Becquerel 2  found  that  the 
phosphorescent  spectra  of  pure  uranyl  chloride  and  of  double  salts  of  uranyl 
and  potassium  or  ammonium  were  quite  different,  and  that  apparently 
the  presence  of  potassium  and  ammonium  caused  the  bands  to  shift  towards 
the  longer  wave-lengths.  The  wave-lengths  of  the  bands  as  given  by 
Becquerel  are: 

1  Compt.  rend.,  142,  205;  1518;   143,  229;   144,  30;  1363:   147,  1472.     Soc.  Fran,  de 

Phys.,  Feb.  6  Q906);  July  6  (1906);  Le  Radium,  June  (1909;. 
J  Ann.  Chim.  Phys.  [4],  27,  539-579  (1872). 


URANIUM   SALTS. 
Phosphorescent  bands. 


119 


1. 

2. 

3. 

4. 

5. 

6. 

7. 

Uranyl  nitrate  .  .  . 

Uranyl  acetate  .  .  . 
Uranyl  chloride  .  . 

6544 
6525 

6180 

6180 
6230 

f  5810  1 
I  5860  / 
5860 
5955 

5590 

5590 
5685 

/  5325  \ 
I  5325  / 
5325 
5433 

5090 

5090 
5176 

4920 

4920 
4980 

Uranyl  sulphate  .  . 

6620 

6262 

5955 

5690 

5418 

5170 

4945 

The  bands  of  the  nitrate  and  acetate  come  at  about  the  same  place  in 
the  spectrum,  whereas  the  chloride  and  sulphate  bands  are  farther  towards 
the  red.  H.  Becquerel !  finds  that  at  low  temperatures  the  phosphorescent 
uranyl  bands  become  quite  sharp  in  the  same  way  that  absorption  bands 
do.  For  uranyl  nitrate  he  gives  the  following  table: 

Phosphorescent  spectrum  of  uranyl  nitrate. 


Room 
temperature. 

Liquid-air 
temperature. 

Room 

temperature. 

Liquid-air 
temperature. 

6210-6150 

6360 

5360-5280 

5327-5320(8) 

6175-6165 

5303-5292(8) 

6145-6127 

5272 

6104 

5240 

6005-6045 

5190 

5940-5840 

5860-5853(s) 

5137 

5837-5830(s) 

5120-5060 

5115 

5782 

5097-5090(8) 

5707 

5074-5070(s) 

5630 

5018 

5600 

4975 

5630-5550 

5585-5575(8) 

4925 

5558-5548(s) 

4893-4855 

4903-4896(8) 

5490 

5435 

5375 

Further  work  has  recently  been  published  by  J.  Becquerel  and  Onnes.2 
At  the  temperature  of  solid  hydrogen  the  intensity  of  emission  is  not  dimin- 
ished and  the  bands  which  existed  at  liquid-air  temperatures  undergo 
further  subdivision.  Lowering  the  temperature  shifts  the  emission  bands 
towards  the  violet.  For  instance,  for  the  double  sulphate  of  uranyl  and 
potassium: 


80°  K 
20°  K 

4904.2 
4903.4 

5114.8 
5113.5 

5342.4 
5341.0 

5590.9 
5588.9 

5863.1 
5860.5 

0.8 

1.3 

1.4 

2.0 

2.6 

The  displacement  of  the  phosphorescent  bands  caused  by  lowering 
the  temperature  from  20°  to  14°  is  very  small,  and  it  is  quite  possible  that 
as  the  temperature  is  lowered  the  bands  approach  asymptotically  a  limiting 


'Compt.  rend.,  144,  459-462  (1907). 

'Commun.  Phys.  Lab.,  Univ.  Leyden,  Nos.  110,  111. 


120 


A    STUDY    OF   THE   ABSORPTION    SPECTRA. 


position.  Becquerel  and  Onnes  find  that  the  difference  in  the  appearance 
of  the  different  groups  of  bands  is  the  result  of  successive  ascending  changes 
in  the  relative  intensities  of  the  bands  in  these  groups.  They  find,  when 
crystals  of  double  salts  are  used,  that  the  spectrum  depends  more  upon  the 
acid  of  the  salt  than  upon  the  other  base.  The  difference  between  the  fre- 
quencies of  two  successive  homologous  bands  is  practically  constant,  not 
only  for  the  same,  but  also  for  all  series  of  homologous  bands  of  the  same 
salt.  The  values  of  this  constant  for  the  various  salts  differ  but  slightly 
from  one  another. 

At  low  temperatures  the  phosphorescent  spectrum  of  uranyl  compounds 
resembles  that  of  the  channeled  spectrum  of  nitrogen  and  carbon.  Bec- 
querel and  Onnes  consider  both  to  have  the  same  character.  Placing  the 
phosphorescing  uranyl  salt  in  a  powerful  magnetic  field  did  not  produce 
any  noticeable  effect  upon  the  uranyl  bands.  Some  of  the  bands  become 
arbitrarily  absorption  or  emission  bands,  and  at  low  temperatures  the 
wave-lengths  are  the  same  for  both  kinds  of  bands.  Following  is  a  table 
giving  the  wave-lengths  of  the  phosphorescent  bands  of  various  uranyl 
salts  at  80°  C. 

The  authors  have  done  a  little  work  on  the  phosphorescent  spectra 
of  uranyl  compounds.  For  the  stimulation  of  the  phosphorescent  bands 
either  sunlight  or  the  light  from  a  spark  has  been  used.  The  glass  screens 
previously  described  or  a  Feuss  monochromatic  illuminator  were  used 
when  only  certain  wave-lengths  of  exciting  light  were  needed.  In  the  case 
of  uranyl  nitrate  it  was  found  that  practically  no  phosphorescence  was 
excited  unless  the  exciting  light  had  a  wave-length  less  than  ^  4900.  For 
all  wave-lengths  less  than  this  phosphorescence  was  excited,  but  the  bands 

Phosphorescent  bands. 


Double  sulphate  of  uranyl 
and  sodium  



(  4891.  5 

5101.2 
5125.4 

5330.0 
5354.7 

5578.5 
5604.6 

Double  sulphate  of  uranyl 
and  ammonium  

Uranyl  sulphate 

(4912.6 
14934.7 
/4918.3 

5124.5 
5147.8 
5133.9 

5355.4 
5380.1 
5369.4 

5607.4 
5633.3 
5626.8 

5881.1 
5908.0 
5910.1 

6184.0 
6215.7 
6219.5 

Uranyl  nitrate  

Double  acetate  of  uranyl 
and  sodium  

4732!5 

4762!3 
4769.2 
47858 

t  

4932!  5 
4950.2 
4964.9 
4972.1 
49902 

5160.2 
5069.6 
5148.6 
5167.8 
5184.9 
5192.2 

5395.8 
5301.5 
5384.5 
5404.5 
5424.0 
5431.6 

5654.0 
5554.6 
5642.7 
5663.4 
5685.8 
5694.6 

5938.8 
5832.9 

4794.6 

4999.2 

5221.4 

5463.5 

seemed  the  same,  irrespective  of  the  wave-length  of  the  exciting  light.  It 
seems  that  the  energy  that  is  absorbed  by  the  series  of  uranyl  absorption 
bands  is  partly  radiated  as  the  energy  of  the  phosphorescent  bands.  This 
suggests  a  number  of  lines  of  work  which  we  hope  to  carry  out  in  the  future. 
Among  these  are  the  following:  Are  the  phosphorescent  bands  of  the  salts 
of  uranyl  affected  in  the  same  way  'as  the  uranyl  absorption  bands?  In 
the  case  of  uranyl  chloride  can  phosphorescent  light  be  excited  by  the 
bands  in  the  region  X  6000?  Does  light  of  wave-lengths  between  that  of 
the  uranyl  absorption  bands  excite  phosphorescence?  In  the  case  of  uranyl 


URANIUM   SALTS. 


121 


nitrate  obtained  from  an  alcoholic  solution   would  light  of  wave-length 
greater  than  X  4900  excite  phosphorescence? 

Different  salts  of  uranyl  phosphoresce  very  differently.  The  speci- 
mens of  uranyl  chloride  gave  very  weak  and  diffuse  bands.  Uranyl  nitrate 
obtained  from  the  evaporation  of  a  methyl  alcohol  solution  showed  no  phos- 
phorescence. Uranyl  bromide  also  gave  very  little  phosphorescent  light 
on  excitation.  Using  the  Hilger  spectroscope,  the  following  approximate 
wave-lengths  for  bands  of  various  salts  were  found : 


Uranyl  sulphate  
Uranyl  nitrate  
Uranyl  acetate  .  .  . 

5660 
5670 

5580 
5600 
5570 

5420 
5410 

5315 
5330 
5340 

5210-5160 
5180 

5085 
5100 
5070 

4950 
4970 

4860 
4840 

The  bands  are  so  hazy  and  wide  that  these  measurements  mean  very 
little. 

Very  little  has  been  done  on  the  fluorescence  of  solutions  of  uranyl 
salts.  Some  work  by  Stokes,  Becquerel,  Morton  and  Bolton,  and  others 
treats  of  fluorescent  bands.  Morton  and  Bolton  give  the  following  wave- 
lengths for  some  of  the  fluorescent  bands  of  the  solid  salts: 


Uranyl  acetate  solid 

6240 

6070 

5760 

5500 

5240 

5030 

Uranyl  chloride,  solid  

6300 

6000 

5660 

5400 

5180 

4930 

Uranyl  monophosphate,  solid.  .  . 
Uranyl  monophosphate,  in  solu- 
tion             

6510 
6470 

6170 
6200 

5850 
5910 

5600 
5650 

5200 
5380 

5100 
5160 

4880 
4920 

4720 
4800 

Uranyl  sulphate 

6520 

6150 

5870 

5600 

5340 

5110 

4890 

4770 

Uranyl  sulphate,  anhydrous.  .  .  . 

6580 

6230 

5930 

5630 

5365 

5145 

4850 

4780 

URANOUS   SALTS. 

Uranium  was  discovered  in  1789  by  Klaproth  and  was  named  to  com- 
memorate the  discovery  of  the  planet  Uranus  by  Herschel  in  1781.  Quite 
a  large  number  of  oxides  are  known. 

The  orange  oxide,  U03(UO20),  or  uranyl  oxide  is  obtained  by  heating 
uranyl  nitrate  slowly  as  long  as  acid  fumes  escape.  When  the  nitrate  is 
rapidly  decomposed  a  red  modification  of  the  oxide  is  produced.  All  the 
uranyl  salts  may  be  considered  as  compounds  of  UO3,  where  one  of  the 
oxygen  atoms  has  been  replaced  by  an  acid  or  halogen  radical.  Aqueous 
solutions  of  the  uranyl  salts  are  partly  hydrolyzed.  The  non-hydrolyzed 
portion  dissociates  in  the  usual  way. 

Urano-uranic  oxide  (U308)  is  obtained  by  heating  uranyl  nitrate  to  a 
high  temperature. 

The  oxide  UO2  is  obtained  by  heating  U3O8  in  a  current  of  hydrogen, 
and  is  of  a  brown  or  copper-red  color.  The  reduction  of  an  oxide  of  uranium 
to  UO2  and  weighing  is  an  analytical  method  of  estimating  uranium.  This 
oxide  in  acid  solutions  forms  the  green  uranous  salts. 

The  oxide  U2O6  is  formed  when  ammonium  uranate  is  strongly  ignited 
in  air.  U04  is  formed  when  a  dilute  solution  of  hydrogen  peroxide  is  added 
to  uranyl  nitrate.  The  uranates  have  the  general  formula  R2U2O7,  as,  for 
example,  potassium  uranate,  K2U2O7.  When  alcohol  is  added  to  a  solution 


122  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

of  hydrogen  peroxide,  uranyl  nitrate,  and  potassium  hydroxide  (a  mini- 
mum amount  of  the  hydroxide),  golden  yellow  needles  crystallize  out  having 
the  composition  (NaO2)2UO4.8H2O. 

Very  little  work  has  been  done  up  to  the  present  on  the  absorption 
spectra  of  uranous  salts,  largely  because  of  their  very  unstable  character 
in  solution.  J.  Formanek  '  describes  the  absorption  spectra  of  uranous 
chloride.  This  was  prepared  by  adding  a  little  zinc  and  hydrochloric  acid 
to  a  uranyl  chloride  solution.  He  found  that  the  spectrum  changed  as  the 
uranyl  chloride  was  being  reduced.  A  very  strong  band  was  found  at 
X  6507.  The  other  bands,  eleven  in  number,  were  U  6722,  6367,  6165,  6030, 
5782,  5497,  5238,  5064,  4962.  4840,  and  4519. 

A  similar  method  has  been  used  by  the  writers.  The  uranous  nitrate, 
sulphate,  and  chloride  were  formed  by  adding  the  corresponding  acid  to  a 
solution  of  the  uranyl  salt  containing  some  zinc.  The  ufanous  chloride 
and  sulphate  were  quite  stable  in  solution,  remaining  reduced  for  weeks. 
Uranous  sulphate  crystallizes  out  from  solution  as  U(SO4)2.9H20.  Solu- 
tions in  alcohol  can  be  reduced  just  as  easily  as  solutions  in  water.  Ura- 
nous nitrate  was  found  to  be  very  unstable.  At  the  present  writing  a  number 
of  spectrograms  have  been  made,  and  much  more  work  will  be  done  on 
these  uranous  salts  and  on  the  absorption  spectra  of  the  various  oxides. 
It  has  already  been  found  that  uranous  chloride 2  has  very  different  spectra 
in  different  solvents. 

URANOUS  CHLORIDE  IN  WATER. 

A  solution  of  uranous  .chloride  in  water  was  made  in  the  usual  way. 
This  solution  was  of  a  dark  green  color  even  when  very  dilute.  When 
sufficiently  dilute  most  of  the  uranous  salt  came  down  as  a  precipitate 
after  standing  for  several  days.  The  solution  was  examined  spectro- 
scopical  y  it  being  practically  colorless  to  the  naked  eye.  The  absorption 
spectra  corresponded  closely  to  that  of  the  uranyl  chloride  bands  of  water. 
e,  f,  and  g  appear  with  considerable  intensity,  while  the  other  bands  are 
very  weak;  e  consisting  of  two  bands  of  about  equal  intensity  and  very 
close  together.  The  wave-lengths  of  the  bands  are  approximately  as  fol- 
lows: A  5030  (weak) ;  a,  A  4910;  6  (very  weak),  A  4790;  c  (very  weak),  X  4550; 
d  (very  weak),  A  4420;  e,  U  4305,  4270;  /,  A  4150,  and  g,  A  4020. 

The  spectrogram  (Plate  84,  A)  represents  the  absorption  of  a  0.17 
normal  solution  of  uranous  chloride  in  water.  Starting  with  the  first  strip 
the  depths  of  cell  are  1.2,  2,  4,  8,  16,  and  32  mm.  For  the  first  three  strips 
the  exposures  were  for  3  minutes  to  the  Nernst  glower  for  all  the  spectrum; 
3  minutes  to  the  ultra-violet,  and  1  minute  to  the  spark.  The  other  three 
strips  were  exposed  to  the  Nernst  glower  for  3  minutes.  The  slit-width  was 
0.15  mm.  and  the  current  in  the  glower  0.9  ampere.  No  exposure  to  the 
ultra-violet  was  made  for  the  upper  strips,  as  it  was  considered  that  this 
region  would  be  entirely  absorbed.  The  spectrogram  shows,  however,  that 
this  would  not  have  been  the  case. 

1  Phys.  Rev.,  29,  555  (1909) ;  30,  279  (1910;.  '  Ibid. 


URANIUM   SALTS.  123 

Strip  1  shows  complete  ultra-violet  absorption  up  to  about  A  3300. 
Two  absorption  bands  JU  4200,  4400  almost  merge  into  each  other.  Of 
these  the  one  with  shorter  wave-length  (A  4270)  is  considerably  stronger 
than  the  other  (A  4370).  A  strong  band  appears  at  A  4980,  about  30  Ang- 
strom units  wide.  This  is  limited  by  a  wide  region  of  general  absorption, 
which  widens  out  very  rapidly  towards  the  vio'et  with  increasing  depth  of 
cell.  This  is  most  likely  due  to  the  presence  of  diffuse  bands  in  this  region. 
The  diffuse  band  at  A  5500  widens  symmetrically  with  increasing  depth  of 
cell.  There  are  two  very  strong  bands  which  for  2  mm.  depth  of  cell  are 
situated  at  A  6430  to  A  6620  and  A  6720  to  X  6770.  This  region  of  ab- 
sorption is  a  very  characteristic  one  for  uranous  chloride  in  water.  Other 
diffuse  bands  appear  at  A  3910,  A  4030,  /I  4600,  and  X  6340. 

URANOUS  AND  ALUMINIUM  CHLORIDES  IN  WATER. 

Uranyl  chloride  was  reduced  in  the  presence  of  an  aluminium  chloride 
solution  of  about  2.4  normal  concentration.  The  concentration  of  uranous 
chloride  was  0.17  normal.  Plate  84,  B,  represents  the  absorption  spectrum, 
the  depths  of  cell  being  1.2,  2,  4,  8,  16,  and  32  mm. 

The  resulting  spectrum  is  very  much  like  that  of  the  pure  aqueous 
solution.  The  ultra-violet  absorption  is  much  greater;  the  absorption 
extending  to  about  A  3800.  The  presence  of  aluminium  brings  out  several 
bands  in  the  blue-violet  region  which  we  shall  continue  to  designate  as  the 
uranyl  bands.  These  bands  have  the  same  wave-lengths  as  the  correspond- 
ing wave-lengths  of  the  uranyl  bands  of  a  solution  of  uranyl  and  alumin- 
ium chlorides  in  water. 

The  band  at  X  5000  is  much  more  diffuse  than  the  corresponding  band 
for  water.  The  band  at  A  5570  widens  symmetrically  with  increasing  depth 
of  cell.  Besides  these  bands  there  are  two  bands  at  A  6550  to  X  6640  and 
A,  6750  to  A  6800.  The  gen  ral  effect  of  the  aluminium  chloride  is  to  bring 
out  the  uranyl  bands;  to  increase  the  ultra-violet  absorption;  to  make  the 
band  A  5000  and  others  slightly  more  diffuse,  and  to  cause  the  uranous 
bands  to  shift  towards  the  red,  about  20  or  30  Angstrom  units. 

The  concentration  of  uranium  in  a  solution  necessary  to  bring  out  the 
uranyl  bands  either  in  the  uranyl  or  uranous  condition  is  about  the  same. 

Spectrogram,  Plate  98,  A,  shows  the  effect  of  the  presence  of  aluminium 
chloride  and  hydrochloric  acid  upon  the  uranous  bands.  Strip  1  represents 
the  absorption  of  a  3  mm.  0.17  normal  solution  of  uranous  chloride  in  water; 
strip  2  the  same  to  which  a  3.04  normal  solution  of  aluminium  chloride 
had  been  added,  so  as  to  make  the  depth  of  cell  4  mm.;  strip  3  a  depth 
of  cell  of  6  mm.;  strip  4  represents  the  same  as  strip  1;  strip  5  is  the 
absorption  of  the  solution  of  strip  4,  to  which  sufficient  hydrochloric  acid 
had  been  added  to  make  a  depth  of  cell  of  16  mm.  Both  aluminium 
chloride  and  hydrochloric  acid  cause  the  ultra-violet  absorption  to  increase 
very  much.  Aluminium  chloride  has  much  the  same  effect  as  hydrochloric 
acid,  although  not  so  great.  It  does  not  change  the  water-bands  A  6400 
and  A  6655  as  does  hydrochloric  acid.  Strip  3  gives  bands  at  the  follow- 
ing positions:  g,  A  4140; /,  A  4280  (strong);  e,  A  4400  (e  and/  almost  merge 
into  each  other);  d,  A  4490;  c,  A  4620;  b,  A  4780,  A  4990,  A  5550,  A  6460  to 
A  6660,  I  6780. 


124 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 


Two  cubic  centimeters  of  a  normal  aqueous  solution  of  uranyl  chloride 
were  added  to  8  c.c.  of  a  3.04  normal  aqueous  solution  of  aluminium  chlo- 
ride and  to  this  were  added  2  c.c.  of  hydrochloric  acid  and  zinc,  so  that  the 
uranyl  salt  was  reduced  to  the  uranous  condition.  To  a  2  mm.  depth  of 
solution  was  added  water  so  as  to  make  the  depth  of  cell  7  mm.  The  addi- 
tion of  water  caused  the  6,  c,  d,  and  e  bands  to  become  very  faint  and 
to  be  shifted  to  the  violet.  The  band  at  A  4980  and  especially  the  bands  at 
>l  5500,  A  6500,  and  A  6750  were  very  considerably  shifted.  The  solution  of 
7  mm.  thickness  showed  bands  at  M  4130,  4210  (narrow),  4285,  4420(7). 

URANOTJS  CHLORIDE  IN  HYDROCHLORIC  ACID  AND  ACETONE. 
A  0.2  normal  solution  of  uranyl  chloride  in  strong  hydrochloric  acid  was 
reduced  by  using  as  little  zinc  as  possible.  Plate  70,  A,  shows  the  absorption 
spectra  of  this  solution  to  which  acetone  has  been  added.  Strip  1  repre- 
sents the  absorption  of  5  mm.  of  the  hydrochloric  acid  solution;  strip  2  the 
same  to  which  1  mm.  of  acetone  has  been  added;  strip  3,  3.3  mm.  acetone, 
and  strip  4,  12  mm.  of  acetone.  The  solution  was  thoroughly  mixed  in 
each  case. 


Strip  1. 

Strip  4. 

a 
6 
c 
d 
e 
f 
9 

4980  (100  A.  U.  wide) 
4800 
4620 
4410 
4280 
4140 
4010 

4925 
4760 
4590 
4425 
4290 
4160 
4040 

20) 
20) 
s)  4535(15) 
s)  4470(f  20)  4380(f  20) 
s)  4340(w20)  4240(w20) 
s)  4200(w20)  4115(w20) 

In  strip  1,  a  consists  of  a  strong  broad  band.  As  acetone  is  added  this 
breaks  into  two  components;  the  longer  wave-length  component  disappear- 
ing as  more  and  more  acetone  is  added.  In  strip  1  the  d  band  has  a  very 
diffuse  band  near  it  on  the  long  wave-length  side.  In  addition  to  the 
uranyl  bands  there  is  a  broad  band  at  A  5550;  one  from  X  6450  to  K  6680 
and  from  X  6720  to  A  6820.  In  strip  4  all  the  broad  uranous  bands  have 
disappeared  and  there  remain  only  fine  bands  from  10  to  20  Angstrom 
units  wide.  These  are  located  at  U  6780,  6740,  6690,  6625,  6600,  6555, 
6490,  6470,  6040,  6000,  5960,  5910,  5220,  5210,  and  5195. 

URANOUS  CHLORIDE  IN  MIXTURES  OF  METHYL  ALCOHOL  AND  WATER  AND  OP  METHYL 
ALCOHOL  AND  ACETONE. 

Plate  89,  A  and  B,  represents  the  absorption  spectra  of  a  constant 
amount  of  uranous  chloride  in  mixtures  of  methyl  alcohol  and  water  (A); 
and  of  mixtures  of  methyl  alcohol  and  acetone  (B);  the  lower  strip  repre- 
senting the  methyl  alcohol  solution. 

As  the  amount  of  water  increases  the  water-band  A  6750  comes  out 
gradually.  The  methyl  alcohol  band  A  5050  to  A  4850  is  probably  double. 
This  narrows  on  the  red  side  into  a  band  at  A  4850.  The  methyl  alcohol 
bands  A  4770  and  A  4600  practically  disappear,  and  the  band  A  4670  becomes 
very  weak.  In  their  places  appear  the  water-bands  >l  4700  and  A  4550. 


URANIUM   SALTS.  125 

The  de  band  of  the  methyl  alcohol  solution  X  4300  to  X  4450  weakens  and 
breaks  up,  giving  the  d  band  at  >l  4400  and  the  e  band  at  X  4280.  This  e 
band  is  a  broadened  band  otherwise  similar  in  appearance  to  the  band 
X  4300  in  methyl  alcohol,  which  appears  quite  narrow.  The  methyl  alcohol 
bands  /,  X  4230,  and  g,  X  4120,  become  the  g  water-band  at  X  4160,  apparently 
by  coming  together. 

The  most  important  change  produced  by  adding  acetone  to  a  methyl 
alcohol  solution  of  uranous  chloride  is  to  bring  in  a  lot  of  narrow  acetone 
bands  in  the  region  >l  6000  to  X  6500,  and  the  strong  absorption  band  from 
X  6500  to  X  6800.  There  also  appears  a  band  at  X  5600. 

URANOUS  CHLORIDE  IN  WATER  AND  ETHYL  ALCOHOL. 

The  addition  of  ethyl  alcohol  (spectrogram  96,  A)  to  an  aqueous 
solution  of  uranous  chloride  causes  a  very  marked  change  in  the  absorption 
spectrum;  the  water-bands  gradually  disappearing  being  replaced  by  ethyl 
alcohol  bands.  This  spectrogram  shows  the  decrease  of  intensity  of  the 
water-bands  very  well.  Strip  2  represents  a  3.2  mm.  depth  of  uranous 
chloride  in  water;  3  the  same  to  which  1.2  mm.  of  ethyl  alcohol  has  been 
added;  4  the  same  as  3  to  which  2.2  mm.  of  ethyl  alcohol  has  been  added; 
5  equals  4  +  6  mm.  ethyl  alcohol,  6  equals  5  +  10  mm.  ethyl  alcohol.  The 
upper  strips  are  weak  on  account  of  the  formation  of  a  precipitate. 

URANOUS  CHLORIDE  IN  ACETONE  AND  WATER. 

Plate  85,  A  and  B,  represents  the  absorption  spectra  of  uranous 
chloride  in  mixtures  of  acetone,  A  representing  the  more  dilute  solution  of 
uranous  chloride.  The  lower  strip  represents  the  absorption  of  an  almost 
pure  acetone  solution,  the  other  strips  representing  the  absorption  of  the 
same  solution  to  which  greater  and  greater  amounts  of  water  are  added. 

This  spectrogram  shows  that  several  of  the  uranyl  bands  are  charac- 
teristic of  acetone  and  aqueous  solutions.  The  absorption  of  an  acetone 
solution  in  the  region  X  6500  is  much  less  and  consists  of  but  a  single  band. 
The  aqueous  solution,  on  the  other  hand,  has  a  very  characteristic  band 
at  X  6750.  The  band  at  X  5550  of  the  acetone  solution  is  shifted  towards 
the  violet  as  water  is  added. 

As  the  percentage  of  acetone  is  decreased  the  acetone  bands  a,  X  4920, 
6,  X  4750,  and  c,  X  4590,  gradually  disappear,  while  the  water-bands  o, 
X  4980,  b,  X  4700,  and  c,  X  4570,  gradually  increase  in  intensity.  No  shift  is 
to  be  noticed. 

The  other  uranyl  bands  appear  but  slightly  changed;  the  positions 
and  intensities  of  the  acetone  and  water-bands  being  about  the  same.  For 
the  acetone  solution  they  are  de,  X  4430,  /,  X  4290,  g,  XX  4160,  4130,  h,  XX  4040, 
4010,  and  i,  X  3910.  For  the  aqueous  solution  they  are  de,  X  4450  (weak), 
/,  X  4290,  g,  X  4150,  and  h,  X  4010. 

URANOUS  CHLORIDE  IN  METHYL  AND  ETHYL  ALCOHOLS. 

In  Plate  88,  A  represents  the  absorption  of  a  dilute  solution  of  uranous 
chloride  in  ethyl  alcohol,  and  B  in  methyl  alcohol.  The  depths  of  cell 
were  3,  6,  12,  24,  and  35  mm.,  slit-width  0.15  mm.,  exposure  to  Nernst  glower 


126  A    STUDY   OF   THE   ABSORPTION    SPECTRA. 

1.5  minutes  to  the  whole  spectrum,  2  minutes  to  the  ultra-violet  of  the 
Nernst  glower,  and  1  minute  to  the  spark. 

The  absorption  for  the  two  solvents  is  very  much  the  same;  the  bands 
being  much  alike  in  intensity  and  position.  The  methyl  alcohol  bands 
are  of  slightly  shorter  wave-length. 

Ethyl  alcohol  solution:  X  4290  (narrow),  >14710,  A  4950  to  >l  5050, 
>l  5280  (weak),  and  4  6200  to  /I  6300. 

Methyl  alcohol  solution:  >t  4000,  J  4130,  X  4250,  ^4290  (narrow), 
>l  4700,  >l  5020,  >l  5260,  and  yl  6150  to  A  6300. 

A  solution  of  the  uranous  chloride  in  methyl  alcohol  stood  for  almost 
a  year.  The  absorption  of  this  solution  was  quite  different  from  that 
described  above.  This  was  probably  due  to  the  much  larger  amount  of 
hydrochloric  acid  and  zinc  chloride  in  the  old  solution;  as  small  amounts  of 
hydrochloric  acid  as  possible  having  been  used  in  the  solution  described 
above.  The  position  of  the  bands  of  the  "old"  solution  were:  ^3910 
(double),  ^  4020  (double),  >l  4130  (double),  /I  4590,  X  4750,  *  4710,  A  5000, 
>l  5550,  and  X  6500  to  A  6800. 

URANOUS  CHLORIDE  IN  GLYCEROL. 

In  making  a  glycerol  solution  of  uranous  chloride  a  strong  solution 
of  uranous  chloride  is  made  in  some  other  solvent.  It  is  then  mixed  with 
glycerol  and  warmed.  The  warming  is  continued  until  as  much  of  the  other 
solvent  is  evaporated  as  possible.  Spectrograms  are  then  made  of  different 
depths  of  this  solution,  and  of  mixtures  of  glycerol  with  some  other  solvent. 
Plate  87,  C,  represents  the  absorption  spectra  of  a  glycerol  solution  of 
uranous  chloride  of  different  depths;  starting  with  the  lowest  strip  the 
depths  being  3,  4,  6,  9,  12,  18,  and  24  mm.  As  the  reduction  was  not  com- 
plete it  is  impossible  to  know  the  concentration  of  the  uranous  chloride, 
although  this  could  be  found  approximately.  The  spectrogram  shows 
the  uranyl  bands  and  the  uranyl  blue-violet  band.  Knowing  the  depth 
of  layer  and  having  made  the  spectrogram  it  is  possible  to  know  quite 
accurately  the  amount  of  uranyl  chloride  in  the  solution.  The  remainder 
of  the  uranium  chloride  is  probably  in  the  uranous  condition. 

The  uranyl  bands,  i,  >l  3800,  h,  1 3930,  and  g,  1 4050,  are  very  weak  and 
about  60  Angstrom  units  broad.  The  band/,  ^  4170,  is  fairly  strong,  as  is 
also  e,  A  4310;  d  is  double,  consisting  of  a  wide  diffuse  band  at  X  4440  and  a 
narrower  diffuse  band  at  X  4530;  c,  A  4680,  and  b,  /I  4840,  are  both  very 
strong,  and  about  80  Angstrom  units  wide;  a,  >l  4980,  is  very  narrow  and 
has  a  very  weak  band  at  about  A  5060.  The  weak  band  at  A  5060  is  barely 
visible  in  the  original  negative.  For  the  greater  depths  of  cell,  bands 
several  hundred  Angstrom  units  wide  and  extremely  diffuse  appear  at 
about  X  5300,  ^  5600,  and  I  6300.  These  will  be  more  fully  discussed  when 
uranous  chloride  in  mixtures  of  glycerol  and  other  solvents  is  described. 

URANOUS  CHLORIDE  IN  MIXTURES  OP  GLYCEROL  AND  WATER. 

Spectrogram,  Plate  86,  A,  represents  the  absorption  of  a  solution  of 
uranous  chloride  in  glycerol  to  which  water  is  added.  Strip  1  represents 
the  absorption  of  a  6  mm.  solution  of  uranous  chloride  in  glycerol;  the  other 


URANIUM   SALTS. 


127 


strip  showing  the  effect  of  adding  water;  the  amount  of  water  added  being 
very  small  for  the  first  few  strips. 

For  strip  1  the  absorption  consists  largely  of  the  bands  a,  X  5000  (very 
broad  and  probably  double),  6,  A  4840;  c,  A  4680;  d,  A  4530,  /1 4440  (latter 
component  very  strong);  e,  A  4310;  /,  A  4170;  and  g,  A 4050. 

The  addition  of  water  causes  the  absorption  in  the  region  A  6250  to 
increase.  There  are  also  broad  absorption  bands  at  X  5000  and  >l  5250, 
which  are  very  diffuse  and  are  somewhat  stronger  for  the  aqueous  solution. 
The  6  glycerol  band  disappears  entirely.  The  c  glycerol  band  breaks  up 
into  two,  and  as  the  amount  of  water  increases  one  of  these  moves  rapidly 
towards  the  violet.  The  stronger  component  remains  practically  station- 
ary. In  strip  7  their  wave-lengths  are  A  4565  (weak)  and  A 4690  (strong  and 
about  30  Angstrom  units  wide).  The  faint  component  of  d  disappears 
and  there  is  left  a  very  diffuse  band  at  about  A  4420.  The  e  band  is  double 
with  components  at  X  4250  and  A  4290.  About  these  components  there  is  a 
very  considerable  amount  of  general  absorption.  The  /  band  is  at  A  4150. 

URANOUS  CHLORIDE  IN  MIXTURES  OF  GLYCEROL  AND  METHYL  ALCOHOL,  GLYCEROL  AND 
ETHYL  ALCOHOL,  AND  GLYCEROL  AND  ACETONE. 

The  addition  of  methyl  and  ethyl  alcohols  causes  very  little  change  in 
the  bands.  Any  large  addition  of  acetone  causes  a  precipitate  to  be  formed. 


Glycerol 
solution. 

Methyl 
alcohol. 

Ethyl 
alcohol. 

Acetone. 

a 

5000 

5000  (broad) 

5000 

SOOO(weak) 

6 

4840 

4815 

4820 

4840 

c 

4680 

4650 

4660 

4680 

d 

(4530 
\4440 

4450  (very 
broad) 

4460 

188}  «" 

e 

4310 

4280 

4280 

4310 

f 

4170 

4140 

4140 

4180 

g 

4060 

4030 

4030 

4055 

URANOCS  CHLORIDE  IN  ACETONE,  IN  METHYL  ALCOHOL,  AND  IN  GLYCEROL. 

Plate  95,  A,  represents  the  absorption  spectra  of  a  solution  of  uranous 
chloride  in  acetone,  the  depth  of  cell  being  1.2,  2,  3,  5,  8,  and  11.5  mm.  The 
slit  was  0.10  mm.  in  width,  current  in  Nernst  glower  0.94  ampere,  exposure 
1.5  minutes  to  glower  and  3  minutes  to  the  spark.  The  bands  are  faint  and 
diffuse.  By  the  addition  of  hydrochloric  acid  they  are  made  very  much 
stronger,  although  the  wave-length  of  the  bands  is  not  changed. 

Plate  95,  B,  represents  the  absorption  spectra  of  uranous  chloride  in 
methyl  alcohol;  the  depths  of  cell  being  2,  4,  6,  8,  and  12  mm.  These  solu- 
tions had  been  made  about  six  months  before  being  used.  Bands  appear 
at  A  6650,  X  6200,  A  5600,  A  5250,  A  4900  to  A  5070,  A  4780,  A  4665,  A  4600, 
A  4230,  and  A  4110.  The  absorption  is  very  strong  throughout  the  region 
A  4200,  and  is  so  general  that  there  is  hardly  any  banded  appearance. 

Plate  95,  C,  represents  the  absorption  of  a  solution  of  uranous  chloride 
in  glycerol  (the  glycerol  also  contained  strontium  chloride).  The  depths 
of  cell  were  2,  4,  6,  8,  12,  and  24  mm.  The  absorption  spectra  show  the 


128 


A    STUDY    OP   THE   ABSORPTION    SPECTRA. 


uranyl  bands,  and  the  large  uranyl  blue-violet  band.  Besides  these  there  is 
a  diffuse  band  at  X  5300  and  a  band  at  A  6200  which  broadens  rapidly  as 
the  depth  of  cell  is  increased.  The  uranyl  bands  are  located  as  follows: 
a,  A  4980;  b,  X  4840;  c,  A  4680;  d,  A  4445  (weak  band  at  A  4530) ;  e,  A  4300, 
to  /,  A  4170. 

UBANOUS  CHLORIDE  IN  METHYL  ALCOHOL  AND  ETHER. 

Two  photographs  were  made,  one  of  uranous  chloride  in  methyl  alcohol 
(next  to  the  spark  spectrum),  and  one  of  uranous  chloride  in  a  mixture  of 
about  60  per  cent  methyl  alcohol  and  40  per  cent  ether.  Further  addition 
of  ether  caused  a  precipitate  to  be  formed  so  that  the  absorption  spectra 
could  not  be  obtained. 

The  methyl  alcohol  solution  showed  complete  ultra-violet  absorption 
to  A  3700.  The  region  A  4300  showed  considerable  general  absorption  due 
to  the  blue-violet  band.  The  following  uranyl  bands  appear:  i,  at  X  3880, 
h,  at  X  4000,  g,  composed  of  two  bands  one  at  A  4110  and  a  narrow  band 
about  10  Angstrom  units  wide  at  A  4135,  /,  of  two  bands,  A  4240  and  A  4285, 
the  latter  being  quite  narrow,  d  and  e  form  one  very  broad  band  at  about 
A  4400,  c  at  A  4610,  and  b  at  A  4780.  Two  bands,  A  4930  (a)  and  A  5050  are 
almost  merged  into  each  other. 

The  addition  of  ether  caused  the  absorption  to  increase;  the  ultra- 
violet absorption  extending  to  A  3800  and  the  absorption  from  A  4100  to 
A  4450  being  almost  complete.  The  uranyl  bands  are  slightly  shifted 
towards  the  red.  Their  general  character  remains  the  same.  The  wave- 
lengths are  approximately,  i,  A  3890,  h,  A  4010,  g,  A  4140,  /,  A  4260,  de, 
A  4440,  c,  A  4630,  6,  A  4790,  a,  A  4960,  and  a  band  at  about  A  5050. 

The  effect  of  ether  is  to  cause  the  bands  to  shift  slightly  to  the  red 
and  to  increase  the  amount  of  absorption. 

EFFECT  OP  THE  PRESENCE  OF  ACIDS  ON  THE  URANOUS  BANDS. 

A  spectrogram  was  made  of  a  3  mm.  solution  of  0.17  normal  uranous 
chloride  in  water  (strip  1).  To  this  was  added  very  strong  hydrochloric 
acid  until  the  depth  of  cell  was  6  mm.  (strip  2),  and  finally  until  it  was 
12.5  mm.  (strip  3),  and  24  mm.  (strip  4). 

The  effect  of  hydrochloric  acid  is  very  marked.  In  general  it  shifts 
the  uranyl  and  uranous  bands  to  the  red.  It  causes  the  uranyl  bands  to 
appear  much  stronger.  In  an  aqueous  solution  the  A  6400  band  is  very 
broad,  and  the  A  6655  band  comparatively  narrow.  Hydrochloric  acid 
reverses  the  appearance  of  these  two  bands;  shifting  both  towards  the 
red  at  the  same  time.  The  following  wave-lengths  give  the  effect  of 
hydrochloric  acid: 


Strip  1. 

Strip  2. 

Strip  1. 

Strip  2. 

b 

4800 

b 

4875 

5000 

c 

4640 

c 

5520 

5620 

d 

4490  (weak) 

d 

6340  (weak) 

e 
f 

4380  (weak) 
4280  (strong) 

4420  (strong) 
4280  (strong) 

e 
f 

6430-6600 
6755 

6500-6570 
6700-6850 

g 

4130 

4150 

9 

URANIUM    SALTS. 


129 


An  aqueous  solution  of  uranous  chloride  in  concentrated  hydrochloric 
acid  gave  the  uranyl  bands  very  distinctly.  The  uranium  salt  was  reduced 
in  this  case  in  the  presence  of  hydrochloric  acid.  The  spectrum  is  almost 
identical  with  that  of  uranous  chloride  when  hydrochloric  acid  is  added 
after  the  reduction  has  taken  place. 

The  addition  of  about  20  per  cent  strong  sulphuric  acid  to  an  aqueous 
solution  of  uranous  and  aluminium  chlorides  has  a  very  marked  effect  upon 
the  bands.  The  general  effect  is  to  shift  the  bands  towards  the  violet. 
For  the  uranous  chloride  solution  containing  aluminium  there  is  a  band 
about  50  Angstrom  units  wide  at  X  6770  and  a  band  from  A  6460  to  A  6640. 
These  are  the  water-bands.  When  sulphuric  acid  is  added  there  is  a  wide 
band  from  A  6600  to  A  6760,  a  narrow  band  at  A  6480,  and  a  wide  band 
running  from  A  6200  to  A  6400.  Sulphuric  acid  reverses  the  breadth  of 
the  two  red  water-bands. 

The  water-band  at  A  5500  is  shifted  to  the  violet  and  doubled  by  the 
addition  of  H2S04,  the  resulting  bands  being  A  5500  (strong)  and  X  5400. 
The  uranyl  bands  are  all  shifted  to  the  violet  as  follows:  a,  A  4990  to  A  4890; 
6,  A  4780  to  A  4750;  c,  A  4620  to  A  4560;  d,  A  4400  (A  4490  weak)  to  A  4360; 
e,  A  4280  to  A  4220;  /,  A  4140  to  A  4080. 

URANOUS    CHLORIDE  IN  WATER  AND  METHYL  ALCOHOL;    WATER  AND  ACETIC  ACID; 
WATER  AND  NITRIC  ACID;  AND  IN  WATER  AND  SULPHURIC  ACID. 

Strip  1,  Plate  98,  B,  is  a  4  mm.  depth  of  layer  of  a  0.17  normal  aque- 
ous solution  of  uranous  chloride;  strip  2  is  the  one  to  which  the  depth  of 
layer  has  been  increased  to  6.3  mm.  by  adding  methyl  alcohol;  strip  3, 
addition  of  methyl  alcohol  until  depth  of  layer  is  7.5  mm.;  strip  4  is  a 
4  mm.  0.17  normal  aqueous  solution  of  uranous  chloride;  strip  5  is  4  to 
which  acetic  acid  has  been  added  to  make  the  depth  of  layer  28  mm.; 
strip  6  is  a  4  mm.  0.17  normal  aqueous  solution  of  uranous  chloride  +  2 
mm.  of  strong  nitric  acid;  strip  7  is  a  4  mm.  0.17  normal  aqueous  solution 
of  uranous  chloride  to  which  19  mm.  of  sulphuric  acid  had  been  added: 


Strip  1. 

Methyl  Alcohol.StripS. 

Acetic  Acid.  Strip  5. 

HNOj.    Strip6. 

HiSOi.    Strip  7. 

6 

e 





4785 
4620 

4750  (very  diffuse). 
4550  (very  diffuse) 

d 



4450 

4400 

/ 

4380 
4280 

4255 

4280-4245 
4130  ft 

4330  e  t 
4240/7 

4340 
4220  (double  narrow 

component  on 

violet  side). 

a 

4130 
4875 

4670  (characteristic) 

4800  (very  diffuse) 

4100 
4900    (wide  and 

5520 

5000  (very  diffuse) 

4900-5000 

5450  (very  diffuse) 

5390-5490°(aLiost 
join). 

6340 
6420-6620 

(5250  (very  diffuse) 
16200  (very  diffuse) 

5500  (very  diffuse) 
6450-6800 

6500  (50  A.  U.  wide) 
6670-6760 

6250-6380  o 
6490    (30  A.U.wide). 
6610-6760  (quite  well 

denned). 

6755 

Plate  90,  A,  strip  1,  represents  the  absorption  of  a  1.8  mm.  solution 
of  uranous  chloride  in  acetone  (a  different  solution  from  that  previously 
described  and  one  which  instead  of  having  been  freshly  prepared  had  been 

9 


130  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

made  about  2  weeks  before  using) ;  strip  2  represents  the  absorption  of  the 
same  solution  to  which  0.5  mm.  hydrochloric  acid  had  been  added;  strip  3  the 
same  as  1  to  which  1.2  mm.  of  hydrochloric  acid  had  been  added  (in  this 
case  a  small  amount  of  a  brown  precipitate  was  formed  causing  the  absorp- 
tion to  be  greatly  increased) ;  strip  4  represents  an  ether  solution  (ether  was 
added  to  the  acetone  solution  of  uranous  chloride,  a  deep  green  precipi- 
tate was  formed,  and  the  ether  became  yellow)  of  probably  uranyl  chloride; 
strip  5  represents  the  absorption  of  an  acetone  solution  of  uranous  chloride, 
freshly  prepared,  2  mm.  in  depth,  strip  6  the  same  5  mm.  in  depth,  and 
strip  7,  14  mm.  in  depth. 

The  freshly  prepared  uranous  chloride  (in  acetone)  solution  shows  the 
uranous  bands  very  faintly.  The  addition  of  hydrochloric  acid  is  seen  to 
bring  out  the  bands  very  well.  In  addition  to  the  bands  already  described 
faint  bands  (strip  2)  appear  at  X  6090,  ^  6340,  ^  6365,  and  ^  6390.  The 
ether  bands  occur  as  follows:  a,  ^4930;  6,  ^4760  (a  faint  component  at 
/I  4800);  c,  ^4600;  d,  ,14440;  e,  >U290;  /,  >U155;  g,  X  4030.  The  relative 
shifts  of  the  ether  bands  relative  to  the  bands  of  the  solution  of  uranous 
chloride  in  hydrochloric  acid  are  very  noticeable  when  the  spectrograms  are 
made  to  overlap.  With  reference  to  these  bands  the  ether  bands  d,  e,f,  and 
g  are  shifted  to  the  red  and  the  a  and  6  bands  to  the  violet. 

URANOUS  CHLORIDE  TO  WHICH  ACETIC  ACID  is  ADDED. 

Plate  94,  B,  represents  a  slightly  acid  solution  of  uranous  chloride  in 
water  to  which  is  added  glacial  acetic  acid  until  there  is  five  times  as  much 
glacial  acetic  acid  present  as  there  was  of  the  original  solution.  The  addi- 
tion of  acetic  acid  causes  a  marked  change  in  the  absorption,  a,  X  4980, 
doubles  into  the  bands  X  5020  and  X  4930;  6  and  c  double  without  being 
changed  very  markedly;  d,  A  4400,  is  slightly  shifted  to  X  4420;  e,  X  4280  to 
A  4300;  /,  ^4140  to  A  4160;  and  g,  A  4010  to  ,U030;  X  5560  is  shifted  to 
X  5590;  X 6450  to  16650  to  X  6500;  and  instead  of  the  band  at  X  6770  there 
are  two  bands  A  6650  and  X  6800. 

UKANOUS  BROMIDE. 

Plate  92,  A,  represents  the  absorption  of  an  0.8  mm.  depth  of  0.5 
normal  uranous  bromide  in  water  to  which  more  and  more  water  has  been 
added.  The  depths  of  cell  are  0.8  mm.,  2.8,  12.5,  22,  and  35  mm. 

The  ultra-violet  absorption  is  but  slightly  changed  by  the  addition  of 
water.  The  other  uranous  bands  are  narrower  the  greater  the  dilution  of 
the  uranous  bromide.  For  the  upper  strip  the  positions  of  the  bands  are 
^4280,  -J4370  (these  bands  form  practically  a  single  band),  >14850  (very 
diffuse),  X  4970  (these  bands  merge  into  each  other),  X  5400  to  X  5600, 
X  6200  to  X  6650  and  X  6750. 

URANYL  AND  URANOUS  ACETATES. 

The  action  of  free  acetic  acid  upon  the  uranyl  absorption  bands  of  an 
aqueous  solution  of  uranyl  acetate  is  quite  small.  The  bands  are  made 
quite  narrow  and  weak.  One  spectrogram  gave  b,  X  4730;  c,  X  4610;  d, 
-U470;  e,  X 4330;  and/,  /14210.  This  is  very  similar  to  the  absorption 


URANIUM    SALTS.  131 

spectra  of  the  anhydrous  salt.  Uranous  acetate  in  water  (Plate  96,  B) 
gives  a  lot  of  weak  diffuse  bands.  The  bands  are  located  at  c,  A  4600; 
d,  >l  4460;  e,  4330;  /,  >l  4200;  and  g,  I  4090.  Besides  these  are  broad  bands 
at  U  5050,  5600,  6700,  and  6850. 

ABSORPTION  SPECTRUM  OF  DRY  URANOUS  ACETATE. 

The  green  precipitate  that  is  formed  when  a  solution  of  uranous  ace- 
tate in  methyl  alcohol  stands  for  several  hours  was  illuminated  by  light 
from  the  Nernst  glower;  the  illuminated  salt  being  over  the  slit  of  the 
spectroscope.  The  green  salt  changed  to  a  dark  color  probably  due  to 
oxidation. 

The  absorption  spectra  showed  weak  diffuse  bands  at  M  4240,  4350, 
4500,  4650,  and  a  wide  band  running  from  X  4900  to  X  5200.  If  these  bands 
are  to  be  identified  as  the/  (I  4240),  e  (X  4350),  d  (A  4500)  and  the  c  (X  4650) 
bands;  and  their  relative  intensities  are  about  the  same  as  that  of  the 
bands  of  uranous  acetate  in  methyl  alcohol;  then  the  bands  are  slightly 
shifted  towards  the  red,  this  shift  being  about  50  Angstrom  units. 

UHANOUS  ACETATE  IN  METHYL  ALCOHOL  AND  ACETIC  ACID. 

To  a  solution  of  uranyl  acetate  in  methyl  alcohol  was  added  glacial 
acetic  acid  and  some  metallic  zinc.  The  solution  becomes  green  in  color 
after  standing  a  few  minutes.  In  an  hour  or  more  a  greenish  precipitate 
is  formed,  and  after  standing  several  hours  the  solution  shows  only  the 
uranyl  bands.  The  plate  represents  the  absorption  spectra  of  the  green 
uranous  acetate.  The  only  variation  here  is  the  depth  of  cell.  For  the 
three  strips  nearest  the  top  the  depth  of  cell  was  the  same. 

Starting  in  the  ultra-violet  the  spectrogram  shows  a  general  absorp- 
tion which  extends  into  the  blue  for  the  greater  depth  of  layer.  No  indica- 
tion of  the  blue- violet  uranyl  band  is  to  be  noticed.  Several  fine  bands 
appear  in  the  blue-violet  region.  As  these  coincide  very  closely  in  position 
with  the  uranyl  acetate  bands  they  will  be  so  considered.  Of  these  the 
a,  b,  c,  d,  e,  f,  and  g  bands  appear.  The  g  band  (X  4070)  is  very  faint. 
The  /  band  (I  4200)  is  stronger  and  is  about  30  Angstrom  units  wide.  The 
c,  d,  e,  and  /  bands  appear  quite  strong;  the  e  band  being  the  strongest. 
It  appears  to  be  complex,  being  composed  of  a  fuzzy  band  at  ^  4285  about 
10  Angstrom  units  wide;  a  fine  sharp  band  at  X  4310  about  3  Angstrom 
units  wide,  and  a  band  extending  roughly  from  {*  J|}|}  to  ^  4340.  The 
d  and  c  bands  (M  4470  and  4610)  are  about  30  Angstrom  units  wide  and  of 
about  equal  intensity.  The  a  and  6  bands  are  very  weak  (>U  4910,  4740) 
and  only  appear  on  the  original  negative. 

The  a  band  with  two  other  very  diffuse  bands  M  5000,  5100  form  the 
wide  absorption  band  in  this  region  and  practically  merge  into  each  other. 
A  similar  band  extends  from  A  5550  to  ^  5650.  In  the  red  there  are  quite 
a  number  of  fine  bands  very  similar  to  the  uranyl  group  in  the  blue  and 
violet.  These  are  very  faint;  the  widest  and  strongest  appearing  at  X  6450; 
this  band  being  about  40  Angstrom  units  wide.  The  other  bands  are  about 
20  Angstrom  units  wide  and  are  located  approximately  at  JJi  6600,  6700, 
6800,  6870,  and  6920. 


132  A    STUDY   OF   THE   ABSORPTION    SPECTRA. 

UBANOUS  ACETATE  IN  GLYCEROL. 

Uranous  acetate  was  obtained  as  already  described.  Some  of  the 
solution  in  methyl  alcohol  and  acetic  acid  was  mixed  with  glycerol  and 
warmed  so  as  to  drive  off  as  much  alcohol  and  acid  as  possible.  The 
solution  was  filtered  hot.  The  precipitate  was  green,  the  filtrate  yellow; 
indicating  that  the  uranium  in  the  glycerol  was  mostly  in  the  uranyl 
condition. 

The  absorption  spectra  showed  several  of  the  uranyl  bands.  These 
bands  are  not  nearly  so  intense  as  the  bands  of  uranous  acetate  in  methyl 
alcohol  and  acetic  acid.  The  /  band  A  4220  appears  to  be  double.  The  e 
band  consists  of  a  band  about  15  Angstrom  units  wide  at  A  4295,  a  band 
at  A  4340,  and  one  at  X  4390;  the  d  band  of  two  bands  A  4480  and  A  4530; 
and  the  c  band  of  X  4630  and  A  4680,  the  latter  being  the  weaker  of  the 
two  bands. 

EFFECT  OF  TEMPERATURE  ON  THE  ABSORPTION  SPECTRA  OF  URANOUS  CHLORIDE. 

A  spectrogram  was  made  to  show  the  effect  of  change  in  temperature 
on  the  absorption  spectrum  of  an  aqueous  solution  of  uranous  chloride. 
To  a  normal  solution  of  uranyl  chloride  in  water  was  added  a  small  amount 
of  zinc  and  hydrochloric  acid.  The  hydrogen  reduced  the  uranyl  chloride 
to  uranous  chloride — a  deep  green  solution  which  seemed  quite  stable. 
The  solution  was  then  placed  in  the  trough  of  the  temperature  apparatus 
and  an  exposure  made  in  the  usual  manner.  The  thickness  of  layer  was 
1  mm.  The  exposures  were  50  minutes  to  the  Nernst  glower  and  4  minutes 
to  the  spark.  The  current  through  the  glower  was  0.8  ampere  and  the  slit- 
width  0.20  mm.  Starting  with  the  strip  nearest  the  comparison  scale  the 
temperatures  were  8°,  17°,  33°,  48°,  62°,  and  73°.  An  exposure  was  made 
at  80°  and  will  be  described  with  the  other  exposures  although  it  is  not  on 
the  spectrogram  as  printed. 

At  8°  a  slight  mist  formed  on  the  prisms  on  account  of  their  low  tem- 
perature and  the  humidity  of  the  air.  For  this  reason  the  strip  is  very  much 
underexposed  and  the  bands  apparently  seem  wider  than  at  the  higher 
temperatures.  At  this  temperature  there  is  complete  absorption  to  A  3650. 
A  blue-violet  absorption  runs  from  A  4050  to  A  4450.  Following  this  are 
three  strong  bands  of  about  equal  intensity  and  each  about  100  Angstrom 
units  wide.  These  bands  are  located  approximately  at  M  4590,  4760,  and 
4970.  Then  comes  a  band  at  about  X  5510,  a  wide  band  from  A  6400  to 
A  6630,  and  a  rather  narrow  band  at  A  6740. 

At  73°  the  spectrum  is  very  similar  to  that  at  8°.  The  amount  of 
absorption  has,  however,  increased  quite  considerably  and  all  the  bands 
have  widened.  The  ultra-violet  band  has  widened  to  A  3800  and  the  blue- 
violet  band  practically  runs  from  A  4050  to  A  5000;  although  there  is  some 
transmission  between  the  bands  /U  4610,  4770,  and  4980.  It  will  also  be 
noticed  that  these  bands  have  been  slightly  shifted  towards  the  red.  This 
shift  is  quite  small,  and  on  account  of  the  haziness  of  the  bands  is  hard  to 
measure  definitely.  None  of  the  other  bands  appear  to  be  shifted.  The 
band  at  A  5500  has  become  about  twice  as  wide  as  it  was  at  the  lower  tern- 


URANIUM   SALTS. 


133 


peratures,  and  the  two  red  bands  have  practically  merged,  running  from 
^  6350  to  A  6800. 

Between  73°  and  80°  the  absorption  has  increased  very  markedly. 
The  whole  spectrum  is  practically  absorbed  up  to  A  5050.  The  band  in 
the  green  runs  from  K  5450  to  >l  5600,  and  the  band  in  the  red  has  also 
widened  very  greatly,  extending  from  ^  6200  to  /I  6800. 

THE  WAVE-LENGTHS  OF  THE  UKANOUS  AND  URANYL  BANDS  UNDER  VARYING  CONDITIONS 
IN  AQUEOUS  SOLUTIONS. 


Uranyl 
nitrate. 

Uranyl 
chloride. 

Uraiious 
bromide. 

Uranyl 
nitrate  in 
HNO». 

Uranous 
chloride. 

Uranyl 
acetate. 

Uranous 
acetate. 

• 

f! 

i! 

p 

rf 

a 
6 
c 
d 

0 

/ 
I 

4870 

4705 
4550 

4310 

4155 
4030 
3905 

4920 

4740 
4560 
4460 

4315 

4170 
4025 

(4970) 
\4880J 
4740 
4600 

4850 

4670 
4520 
4380 

4240 

4140 
4050 
3920 

4980 

4790  to 
4550  w 
4420  w 
<  43051 
U270/ 
4150 
4020 
3910 

4910 

4740 
4600 
4460 

4310 

4160 
4070 
3970 

4600 
4460 

4330 

4200 
4090 

4880 

4720 
4560 
4450 

4280 
4160 

4910 

4740 
4595 
4455 

4310 

4160 
4070 
3970 

4900 

4740 
4580 
4460 

4330 

4200 
4070 
3970 

t 

3815 

3810 

3830 

3830 

3850 

1 

3710 

3750 

3740 

i 

3605 

3670 

3630 

I 

3515 

3590 

3530 

m 

6740 
6480 
5500 

3520 

5500 
6500 
6750 
6340 

5050 
5600 
6700 
6850 

ALCOHOLIC  SOLUTIONS  OP  URANIUM  SALTS. 


Uranous  chloride  in  methyl  alcohol  gives  bands  at  M  6650,  6250,  5600, 
5260,  4900-5070,  4780,  4665,  4600,  4230,  4410. 

Uranous  bromide  in  methyl  alcohol  gives  bands  at  M  6650,  6200,  5650- 
5500,  5250,  4950-5100,  4680S,  4450-4300,  4150. 


Uranous 

Uranyl 

Uranous 

Uranyl 

Uranous 

Uranyl 

Uranous 

Uranyl 

Uranous 

Uranyl 

Uranous 

chloride 

nitrate 

acetate 

nitrate 

chloride 

acetate 

bromide 

chloride 

chloride 

chloride 

chloride 

in 

in 

in 

in 

in 

in 

in 

in 

in 

in 

in 

methyl 
alcohol. 

methyl 
alcohol. 

methyl 
alcohol. 

ethyl 
alcohol. 

ethyl 
alcohol. 

methyl 
alcohol. 

methyl 
alcohol. 

methyl 
alcohol. 

methyl 
alcohol. 

ethyl 
alcohol. 

ethyl 
alcohol. 

5050 

5000 

5050  to 

4880 

5070 

a 

4930 

4930 

4910w 

4950 

4900 

4900 

4930 

5000 

4900 

5000 

b 

4780 

4760 

4740w 

;  v(  K  ) 

4710 

4720 

4780 

4760 

4815 

4750 

4820 

e 

4610 

4610 

4610 

4630 

4590 

4665 

4610 

46506 

4580 

4665 

d\ 

44006' 

4455 

4470 

4475 

4450 

4465 

4450 

4400 

4460 

f 

4285 

4325 

4330 

4325 

4320 

4345 

a 

4135) 
4110J 

4190 

f4310) 
14285/ 

4180 

4290u 

4190 

4230 

4220 

4280 

4250 

4280 

h 

4000 

4070 

4200 

4080 

4070 

4110 

4090 

4140 

4100 

4140 

i 

3965 

4070 

3970 

3980 

3980 

4030 

3980 

4030 

j 

3855 

3875 

3860) 
3760J 

3860 

6260 

5280 

6250 

6250 

» 6  is  broad. 


134 


A    STUDY   OF   THE    ABSORPTION    SPECTRA. 


GLYCEROL  SOLUTIONS. 


Uranous 
acetate  in 
glycerol. 

Uranous 
bromide 

glycerol. 

Uranyl 
chloride  in 
glycerol. 

Uranyl 
chloride 
in 
glyoerol. 

Uranyl 
nitrate 
in 
glycerol. 

Uranous 
sulphate  in 
glycerol. 

Uranous 
chloride 
in 
glycerol. 

Urauous 
chloride  in 
glycerol. 

5060  W 

5050 

f  5040 

\ 

.... 

\5020 

i 

b 

4680  \  ,  . 
4630  }  w 

....    { 

4980  w 
4840s80* 

4900 

4910 
4750 

•14780 

/5000 
\4790 

5000 
4840 

c 

4530  X 
4480  / 

4700? 

4680s80 

4720 



4640 

4680 

d 

4390) 
4340V 
4295  J 

4550u>? 

4530  n.d.3 
4440  w 

4540 
4400 

J4480 

/4550 
\4420 

4530  w> 
4450 

e 

4220 

4300 

4260 

4350 

4365 

4300 

4310 

f 

4200? 

4170 

4140 

4220 

4250 

4170 

4260  w;.  10 

g 

4050  w 

4025 

4100 

4120 

4050 

4170 

I 

3930  w 

3920 

3970 

4010 

i 

3800  w 

3900 

i 

3750 

i 

3650 

1  w  means  weak .        2  *  =  strong,  80  =  A .  U .        *n.d.  =  narrow  and  di ff use. 

URANYL  SALTS  IN  THE  PRESENCE  OF  FREE  ACID. 


Uranoua 
chloride  in 
water. 

Uranous 
gloride  with 
rdrochloric 
acid. 

Uranyl  acetate 
in  acetone 
with  acetic 
acid. 

Uranyl 
acetate  in 
water. 

Uranyl 
acetate  with 
acetic  acid. 

Uranous 
acetate  in 
water. 

a 

4980 

5000 

4910 

b 

4790 

4800 

4620? 

4740 

4730 

. 

c 

4550 

4630 

4460? 

4595 

4610 

4600 

d 

4420 

4430 

4330? 

4455 

4470 

4460 

e 

f  4305  \ 
\  4270  / 

4270 

4220? 

4310 

4330 

4330 

f 

4150 

4140 



4160 

4210 

4200 

g 

4020 

4020 

4070 

4030 

h 

3910 



3970 

3830 

6770 

6550 

5620 

EFFECT  OF  THE  PRESENCE  OF  FOREIGN  SALTS. 


chloride  in 
water. 

3fi& 

+  A1CU 

Uranyl 
chloride 
+  ZnClj 

Uranous 
chloride 
+A1CU 

Uranous 
chloride 
+  H*S04 

a 

4920 

4950 

4930 

4990 

4890 

b 

4740 

4790 

4770 

4780 

4750 

c 

4560 

4620 

4600 

4620 

4560 

d 

4460 

4480  to  4420 

4400 

f4490\ 
\4400i 

4360 

e 

4315 

4245 

4280 

4220 

f 

4170 

4270 

4115 

4140 

4080 

9 

4030 

4135 

h 

4010 

i 

URANIUM   SALTS. 
EFFECT  OF  FREE  ACID. 


135 


Uranyl 
nitrate 
in 

Uranyl 
nitrate 
to  which 

Uranyl 
sulphate 
in 

Dry 
uranyl 
nitrate 

Uranyl 
sulphate 

Uranyl 
nitrate 
in 

sra1. 

in 

+ 

water. 

Hadd°ed8 

water. 

HNOi. 

H,SO«. 

HNO». 

water. 

HC1. 

a 

4870 

4925 

4900 

4850 

4930 

4790 

4920 

4950 

6 

4705 

4750 

4740 

4670 

4750 

4670 

4740 

4800 

c 

4550 

'4560 

'4580 

4520 

'4560 

4510 

4560 

4635 

d 

4380 

4460 

4380 

4380 

4370 

4460 

4480 

e 

4316 

4240 

4330 

4240 

4240 

4230 

4315 

4420 

f 

4155 

4100 

4200 

4140 

4100 

4125 

4170 

4280 

g 

4030 

4070 

4050 

4000 

4025 

4050 

h 

3905 

3980 

3970 

3920 

3980 

3900 

4015 

i 

3815 

3870 

3850 

3810 

3870 

3790 

j 

3710 

3770 

3740 

3750 

3770 

3670 

k 

3605 

3660 

3630 

3670 

3660 

3570 

I 

3515 

3560 

3530 

3590 

3560 

3520 

1  Double. 


Any  small  differences  in  the  wave-lengths  of  the  absorption  bands  of 
uranous  solutions  under  different  conditions  are  probably  due  to  the 
presence  of  varying  amounts  of  zinc  used  in  reducing  the  uranyl  to  the 
uranous  condition. 


CHAPTER  XII. 

GENERAL  DISCUSSION  OF  RESULTS. 

Previous  investigators  have  in  many  instances  spoken  of  the  absorp- 
tion of  light  by  molecules,  ions,  or  aggregates  of  these.  The  present  theory 
of  spectroscopy  is,  however,  more  and  more  inclined  to  consider  the  nega- 
tive electron  as  the  chief  absorber  of  light  in  the  visible  and  ultra-violet 
portions  of  the  spectrum.  Whether  the  absorbing  electron  is  the  same  as 
the  electron  found  in  vacuum  discharge  tubes,  or  emitted  by  radioactive 
elements,  is  at  present  a  very  much  discussed  subject.  It  seems  to  be 
quite  certain  that  the  masses  of  many  of  the  absorbers  are  not  of  molecular 
magnitude.  It  is  equally  certain,  as  experiments  show  and  as  theory  indi- 
cates, that  the  various  coefficients  which  define  the  equations  of  motion 
of  the  absorber  are  functions  of  the  conditions  under  which  the  absorbers  exist. 
If  the  absorbers  are  electrons  we  may  think  of  them  as  being  within  or  in 
close  proximity  to  the  atom.  Such  absorbers  would  be  expected  to  have 
their  period,  coefficient  of  damping,  and  other  coefficients  greatly  modified 
by  the  formation  of  aggregates,  solvates,  etc.,  and  such  seems  to  be  the 
case.  According  to  the  present  theory  of  the  conductivity  of  solutions 
it  would  be  expected  that  if  the  absorbers  existed  in  or  about  the  atom, 
their  properties  would  be  very  greatly  affected  by  the  given  atom  existing 
in  an  ionic  or  in  a  condition  as  part  of  a  molecule.  Consequently,  at  great 
dilutions,  it  would  be  expected  that  the  absorption  of  a  colored  solution  of 
a  salt  would  be  entirely  independent  of  the  salt  when  the  anion  was  the 
carrier  of  the  absorbers.  In  the  absorption  spectra  of  solutions  there  are 
but  few  examples  where  the  absorption  spectra  of  different  salts  with  the 
same  cation  are  very  different  from  each  other.  There  is  one  important 
exception  in  the  case  of  aqueous  solutions  of  the  uranyl  salts.  The  uranyl 
nitrate  bands  are  all  of  shorter  wave-lengths  than  the  bands  of  the  other 
uranyl  salts.  The  absorption  spectra  of  these  salts  have  been  photographed 
by  us  over  quite  wide  ranges  in  concentration,  and  no  evidence  has  been 
obtained  that  indicates  any  dependency  of  the  wave-lengths  of  the  uranyl 
bands  on  the  concentration. 

Although  more  and  more  spectroscopic  phenomena  are  being  explained 
by  means  of  the  electron  theory,  yet  there  is  a  general  tendency  to  consider 
that  only  the  electrons  in  a  few  atoms  are  in  a  condition  to  absorb  or  emit 
light  at  any  moment.  What  the  nature  of  these  conditions  is,  is  at  present 
not  well  known,  but  it  seems  probable  that  they  are  exceptional  states  in 
some  cases  at  least.  For  instance,  only  a  few  of  the  sodium  atoms  take 
part  in  the  absorption  of  the  D  lines  at  any  particular  time,  and  the  same 
is  probably  true  of  neodymium  and  erbium  salts  in  solution  or  in  the  solid 
state.  It  is  supposed  by  some  physicists  that  absorption  or  emission  may 
take  place  during  ionization,  as,  for  example,  when  an  electron  leaves  or 
returns  to  an  ion.  Upon  a  basis  such  as  this  is  laid  the  theories  of  dynamic 
isomerism,  isorepesis,  and  Stark's  theory  of  the  spectrum  of  canal  rays 

137 


138  A    STUDY   OF   THE   ABSORPTION   SPECTRA. 

and  of  fluorescence.  On  such  a  theory  as  this  it  may  be  supposed  that  in 
solutions  the  absorption  took  place  in  those  molecules  that  are  undergoing 
dissociation,  or  in  those  ions  that  are  combining  to  form  molecules.  In 
the  case  of  the  uranyl  nitrate  bands  it  was  pointed  out  that  the  combined 
action  of  water  and  the  N03  group  had  a  hypsochromous  effect  upon  the 
wave-lengths  of  these  bands.  That  it  is  due  to  the  combined  action  of  the 
water  and  the  NO3  group  is  shown  by  the  fact  that  in  other  solvents  the 
NO3  group  does  not  have  this  hypsochromous  effect;  while  in  water  it  is 
only  the  nitrate  bands  that  have  the  smaller  wave-lengths.  According  to 
the  theory  of  dynamic  ionization  the  absorption  of  light  could  take  place 
while  the  NO3  groups  were  near  the  UO2  group,  so  that  the  periodicity  of 
the  absorbed  light  would  be  affected.  According  to  this  theory,  however, 
the  number  of  ionizations  through  which  a  molecule  would  pass  would 
probably  be  a  function  of  the  concentration;  and  thus  the  intensity  of  the 
absorption  bands  should  be  a  function  of  the  concentration.  But  for  ura- 
nyl nitrate  Beer's  law  holds  at  least  approximately,  whereas  considerable 
variations  would  be  expected  from  the  above  theory.  If  the  absorption 
takes  place  during  periods  of  ionization,  and  the  intensity  of  the  absorption 
depends  only  on  the  number  of  these  ionizations,  then  the  fact  that  Beer's 
law  holds  shows  that  the  number  of  these  ionization  phenomena  is  inde- 
pendent of  the  concentration.  The  fact  that  the  absorption  spectrum  of 
uranyl  nitrate  crystals  is  very  similar  to  solutions  indicates  that  the  uranyl 
groups  that  take  part  in  absorption  are  about  as  closely  united  with  water 
and  the  N03  group  in  solution  as  they  are  in  the  solid. 

It  may,  however,  be  said  in  general,  that  the  anions  of  the  various  col- 
ored salts — and  in  practically  all  cases  it  is  the  anion  that  exhibits  banded 
absorption — play  a  much  less  important  role  in  modifying  the  spectra  than 
the  solvent.  Different  salts  of  the  same  anion  in  the  same  solvent  usually 
have  the  same  absorption  spectra.  On  the  other  hand,  the  absorption 
spectra  of  the  powdered  salts  themselves  may  be  very  different.  This  fact 
shows  that  the  solvent  plays  a  most  important  part  in  the  absorption,  and  it 
seems  highly  probable  that  in  a  large  number  of  cases  there  is  an  "  atmosphere  " 
of  the  solvent  molecules  about  the  colored  absorber.  In  a  word,  there  is  solva- 
tion.  However,  in  the  case  of  the  nitric  oxide  *  spectrum  it  seems  possible 
to  have  the  gas  existing  in  solution  and  at  the  same  time  having  its  ab- 
sorption spectra  unaffected.  The  nitric  oxide  spectrum  only  occurs  under 
very  special  conditions,  and  has  not  thus  far  been  obtained  for  solutions 
of  the  gas,  but  only  when  some  acid  is  added  to  nitric  acid  or  a  nitrate. 
It  would  seem  probable  that  in  this  case  no  chemical  reaction  or 
"  atmosphere  "  of  the  solvent  existed. 

Whereas  the  absorption  of  different  salts  of  the  same  colored  anion  is 
in  general  very  similar,  on  the  other  hand,  the  absorption  spectra  of  the 
same  salt  in  different  solvents  are  often  very  different  indeed.  Formerly  this 
effect  of  the  solvent  was  thought  to  be  due  to  a  difference  in  the  value  of  the 
dielectric  constant,  but  Jones  and  Anderson  have  pointed  out  that  the 
most  probable  cause  is  the  formation  of  solvates,  or  more  or  less  stable  com- 

1  Phys.  Rev.,  30,  279  (1910). 


GENERAL    DISCUSSION   OF    RESULTS.  139 

pounds  of  the  salt  and  solvent.  The  reason  for  this  conclusion  is  that  in  mix- 
tures of  two  solvents,  each  set  of  solvent  bands  appears;  the  intensity  of  any 
solvent  band  being  a  function  of  the  relative  amounts  of  the  solvents  present. 
That  these  compounds  or  solvates  have  a  definite  composition  seems  to 
be  indicated  by  the  fact  that  for  most  of  the  neodymium,  uranyl,  and 
uranous  salts  there  appears  only  a  single  set  of  "solvent"  bands  for  each 
solvent;  and  in  mixtures  of  these  solvents  in  most  cases  but  two  sets  of 
bands  are  necessary  to  explain  the  results.  The  persistence  of  solvent 
bands  varies  quite  widely  for  the  different  solvents,  and  appears  to  be  great- 
est for  water  and  glycerol  and  less  for  the  alcohols.  This  persistence  of 
any  one  solvent  band  seems  to  be  the  same  for  quite  widely  different 
salts.  There  are,  however,  some  cases  where  it  may  be  possible  that  inter- 
mediate solvates  are  formed.  Neodymium  chloride  dissolved  in  mixtures 
of  water  and  glycerol  seems  to  indicate  that  the  "water"  band  /I  4274 
gradually  shifts  to  the  "  glycerol  "  bands. 

Probably  no  salts  show  more  characteristic  bands  than  some  of  the  ura- 
nous salts  in  the  various  solvents:  water,  the  alcohols,  acetone,  and  glycerol.  It 
seems  probable  that  the  absorbers  are  the  same  for  the  corresponding 
bands  of  any  two  "solvent"  spectra.  An  important  fact  indicating  this 
is  given  by  Becquerel,  who  found  the  Zeeman  effect  to  be  the  same 
when  different  solvents  of  the  same  salt  were  used.  It  is  generally  conceded 
that  at  higher  temperatures  solvates  are  broken  up.  At  present,  work  is 
being  done  on  solutions  containing  mixtures  of  two  solvents  in  such  pro- 
portion as  to  give  both  sets  of  solvent  bands.  As  the  critical  temperature 
of  one  solvent  is  approached,  according  to  the  foregoing  theory,  the  bands 
of  that  particular  solvent  should  disappear.  In  many  cases  the  two  sets 
of  solvent  bands  differ  not  only  in  wave-lengths  but  also  in  intensity, 
and  in  the  number  of  components.  Of  all  the  bands  of  the  neodymium 
absorption  spectra,  the  "  water  "  band  A  4274  is  one  of  the  strongest,  and 
one  that  is  freest  from  neighboring  bands.  Yet,  in  different  solvents  this 
band  may  become  a  doublet,  a  triplet,  or  may  even  apparently  break  up 
into  a  whole  series  of  bands.  It  is  quite  certain  that  when  the  mechanism 
of  these  changes  is  known,  our  knowledge  of  chemical  compounds  will  be 
increased  very  greatly,  and  it  is  very  important  that  gradual  changes  of  sol- 
vent or  salt  may  be  made  at  low  temperatures  where  the  bands  are  much 
sharper,  and  work  is  now  in  progress  on  this  problem. 

In  some  cases  it  is  possible  to  break  up  the  absorption  bands  by 
chemical  methods  into  very  fine  bands.  A  very  striking  example  is  the 
case  of  uranyl  and  uranous  salts  in  acetone  solutions.  The  uranyl  salt  in 
acetone  gives  six  bands  in  the  region  ^  5000  that  are  characteristic  of 
acetone  solutions.  By  the  addition  of  hydrochloric  acid  to  an  acetone 
solution  the  uranyl  bands  are  broken  into  fine  components.  Several  of 
the  uranyl  bands  become  triplets  and  some  doublets.  But  the  most  marked 
example  is  the  addition  of  hydrochloric  acid  to  an  acetone  solution  of 
uranous  chloride.  Several  very  broad  uranous  bands  are  broken  up  into 
a  number  of  very  fine  and  quite  intense  bands. 

One  very  interesting  result  has  come  to  light  from  the  examination  of 
the  effect  of  free  nitric  acid  on  the  absorption  spectra  of  uranyl  nitrate; 


140 


A    STUDY   OF   THE   ABSORPTION    SPECTRA. 


of  sulphuric  acid  on  the  sulphate;  acetic  acid  on  the  acetate;  or  hydro- 
chloric acid,  calcium,  or  aluminium  chloride  on  the  chloride.  In  general 
the  presence  of  these  foreign  reagents  causes  the  uranyl  bands  to  become  more 
intense  and,  in  most  cases,  narrower.  The  action  of  all  the  above  reagents 
except  nitric  acid  is  to  cause  the  uranyl  bands  to  be  shifted  towards  the  red. 
Nitric  acid,  however,  causes  large  shifts  towards  the  violet.  The  above 
reagents  have  a  similar  effect  on  the  corresponding  uranous  bands. 

The  explanation  of  the  above  effects  seems  possible  by  supposing  that 
aggregates  are  formed.  In  the  case  of  neodymium  salts  the  effect  of  the 
above  reagents  is  very  small,  and  nitric  acid,  instead  of  causing  the 
neodymium  nitrate  bands  to  become  narrower,  stronger,  and  to  be  shifted 
towards  the  violet,  simply  causes  the  bands  to  become  much  more  diffuse. 
The  other  reagents  cause  the  neodymium  bands  to  become  diffuse,  weaker, 
and  to  broaden  somewhat  towards  the  red. 

In  addition  to  trying  the  effect  of  acids  upon  uranium  salts  of  the  same 
acid,  spectrum  photographs  were  made  of  the  effect  produced  by  adding  acids 
to  different  uranyl,  uranous,  and  neodymium  salts.  Uranyl  nitrate  was 
treated  with  sulphuric,  hydrochloric,  and  acetic  acids;  uranyl  and  uranous 
acetates  with  various  acids;  various  uranous  salts  and  neodymium  acetate 
with  nitric  acid.  These  salts  and  acids  were  selected,  since  they  showed 
the  greatest  spectroscopic  changes.  Especially  interesting  are  the  spec- 
trograms made  by  treating  uranous  salts  with  nitric  acid. 

The  spectrophotographs  of  chemical  reactions  show,  invariably,  that  the 
changes  produced  in  the  spectra  as  one  salt  is  transformed  into  another  are 
gradual,  whereas  in  changing  the  solvent  this  is  not  the  case.  For  instance, 
when  uranyl  nitrate  is  transformed  into  uranyl  sulphate,  the  uranyl  nitrate 
bands  gradually  shift  into  the  sulphate  position.  The  same  effect  is  produced 
when  solutions  are  made  containing  different  amounts  of  uranyl  nitrate 
and  uranyl  sulphate.  Further  addition  of  sulphuric  acid  causes  the  bands 
to  shift  still  more.  An  example  is  given  where  to  a  small  amount  of  a 
solution  of  uranyl  nitrate  in  nitric  acid  a  large  amount  of  sulphuric  acid 
is  added. 


Nitrate  in 
nitric  acid. 

Same  plus 
sulphuric  acid. 

Nitrate  in 
nitric  acid. 

Same  plus 
sulphuric  acid. 

a 

4850 

4930 

h 

3920 

3980 

b 

4670 

4750 

^ 

3810 

3870 

c 

'4520 

24560 

j 

3750 

3770 

d 

4380 

4380 

k 

3670 

3660 

e 

4240 

4240 

I 

3590 

3560 

f 

g 

4140  \ 
4050  / 

4100 

1  Narrow. 


!  Double. 


It  will  be  seen  that  the  shifts  in  these  cases  are  quite  large,  and  the 
moving  together  of  the  /  and  g  bands  is  especially  remarkable.  The  chem- 
ical changes  studied  thus  far  spectroscopically  have  been  in  most  cases 
confined  to  aqueous  solutions.  Changes  effected  in  other  solvents  are  usu- 
ally smaller.  For  instance,  the  addition  of  sulphuric  acid  to  a  glycerol 


GENERAL    DISCUSSION   OF   RESULTS.  141 

solution  of  uranous  sulphate  simply  causes  the  g,  h,  and  i  bands  to  be  shifted 
about  20  Angstrom  units  to  the  violet.  Similar  changes  are  often  produced 
by  adding  salts  containing  the  cation  of  the  acid.  For  instance,  it  has  been 
found  that  the  absorption  spectra  of  uranyl  chloride  in  a  concentrated 
aqueous  solution  of  aluminium  chloride,  or  zinc  chloride,  or  hydrochloric 
acid  are  very  similar  to  that  of  uranyl  and  calcium  chlorides  in  methyl 
alcohol,  or  of  uranyl  chloride  in  ethyl  alcohol. 

When  nitric  acid  is  added  to  an  aqueous  solution  of  uranous  acetate, 
it  is  found  that  the  oxidation  of  the  uranous  salt  does  not  occur  when  small 
amounts  of  acid  are  added,  but  that  in  this  case  the  uranous  bands  are 
shifted  to  the  violet.  The  uranyl  bands  pass  through  several  stages  and 
change  very  greatly,  indicating  that  the  chemical  reaction  is  quite  complex. 

The  absorption  spectra  of  uranous  salts  usually  show  the  uranyl 
bands,  and  in  some  cases  these  are  very  strong.  The  question  immediately 
arises  as  to  whether  the  uranyl  bands  are  common  both  to  the  uranyl  and 
uranous  salts.  It  seems  probable  that  they  are  characteristic  of  only  the 
uranyl  salts,  although  this  is  not  certain.  Uranous  salts  have  been  obtained 
which  show  only  a  strong  band  appearing  in  about  the  same  position  as 
that  of  the  blue-violet  uranyl  band,  and  this  indicates  that  the  presence 
of  uranyl  bands  is  due  to  the  uranyl  salt  which  has  not  been  reduced. 
In  most  of  the  changes  of  solvent  and  salt  it  has  been  found  possible  to 
follow  the  individual  uranyl  bands  throughout  the  reactions  which  took 
place,  and  this  seems  to  indicate  that  the  absorption  is  due  to  a  system  of 
some  kind  which  preserves  its  entity  throughout  all  these  changes. 

The  gradual  shift  of  the  absorption  bands  as  one  salt  of  a  metal  is  trans- 
formed into  another  salt  by  the  addition  of  more  and  more  free  acid  is  very 
important. 

The  work  already  done  in  this  laboratory  on  the  absorption  spectra 
of  solutions,  in  which  about  five  thousand  solutions  have  now  been  studied, 
shows  that  any  given  series  of  absorption  bands  probably  correspond  to  a 
definite  chemical  condition  of  the  dissolved  substance.  When  a  salt  is 
treated  with  a  free  acid  the  absorption  bands  of  some  of  the  salts  shift  grad- 
ually over  to  the  position  occupied  by  the  bands  corresponding  to  the  new 
salt  of  the  metal  with  the  acid  in  question.  In  an  example  of  this  kind  the 
bands  can  be  made  to  occupy  any  position  between  the  initial  and  final  posi- 
tions, and  it  seems  probable  that  when  a  salt  of  one  acid  is  transformed  in 
this  way  into  a  salt  of  another  acid,  there  is  a  whole  series  of  intermediate 
systems  or  compounds  formed.  These  are,  for  the  most  part,  too  unstable 
to  be  isolated  by  the  methods  at  present  at  our  disposal,  but  their  action 
on  light  makes  their  existence  in  solution  highly  probable. 

It  is  well  known  that  our  chemical  equations  represent,  in  general,  only 
the  beginning  and  end  of  chemical  reactions,  and  tell  us  nothing  about  the 
intermediate  stages  of  the  reaction,  which  are,  of  course,  the  most  interest- 
ing parts  of  the  reaction.  The  results  obtained  in  this  work  make  it 
highly  probable  that  chemical  reactions  may  sometimes  be  much  more  com- 
plex than  would  be  indicated  by  the  equations  that  we  ordinarily  use  to  express 
them.  When,  for  example,  a  nitrate  is  transformed  into  a  sulphate,  there 
seems  to  be  a  series  of  intermediate  systems — nitrosulphates  or  sulpho- 


142  A    STUDY    OF    THE   ABSORPTION    SPECTRA. 

nitrates  formed,  about  which  we  know  nothing  chemically,  but  whose 
existence  is  shown  by  a  purely  physical  method — the  action  of  these  sub- 
stances on  light. 

Whether  we  shall  ever  be  able  to  deal  with  these  substances  chemically, 
it  is  impossible  at  present  to  predict  on  account  of  their  comparative  in- 
stability; the  most  hopeful  methods  of  studying  them  being  the  physical 
chemical,  which  can  investigate  their  properties  while  in  solution  in  the 
different  solvents. 

Rise  in  temperature  causes  the  general  absorption  of  any  salt  in  water 
to  increase,  and  also  causes  the  bands  to  broaden  and  become  more  intense. 

The  increase  in  the  general  absorption  with  rise  in  temperature  is 
much  greater  for  concentrated  solutions.  This  also  holds  true  for  bands 
of  the  second  type,  and  to  a  small  extent  for  bands  of  the  third  type. 

The  presence  of  calcium  and  aluminium  chlorides  causes  the  chromium 
chloride  bands  to  widen  very  unsymmetrically  on  the  long  wave-length 
edge  with  rise  in  temperature. 

The  uranyl  chloride  bands  are  shifted  towards  the  red  with  rise  in 
temperature.  No  shift  for  the  uranyl  nitrate  could  be  detected.  Uranyl 
nitrate,  however,  dissolved  in  strong  nitric  acid  showed  quite  a  large  shift. 
The  uranyl  acetate  and  sulphate  bands  were  slightly  shifted. 

No  shift  with  rise  in  temperature  was  noticed  for  solutions  of  neodym- 
ium  or  erbium  salts.  When  calcium  chloride  is  present  the  neodymium 
chloride  bands  are,  however,  shifted,  and  the  remarkable  fact  is  observed 
that  the  bands  then  become  fainter  with  rise  in  temperature.  This  latter 
phenomenon  is  considered  to  be  very  important,  and  it  may  be  that  the 
abnormal  Zeeman  effect  observed  by  Becquerel  is  due  to  the  presence  of 
foreign  compounds  in  the  tysonite  and  xenotine  crystals. 

BEARING  OF  THE  SOLVATE  THEORY  OF  SOLUTION. 

So  much  evidence  has  now  been  accumulated  for  the  general  correct- 
ness of  the  theory  of  solvation  in  solution,  or  combination  of  solvent  and 
dissolved  substance,  that  there  can  scarcely  exist  any  reasonable  doubt  as 
to  it  representing  a  great  truth  of  nature.  Such  being  the  case,  the  ques- 
tion arises  whether  it  helps  us  in  dealing  with  the  phenomena  presented 
by  solutions? 

When  the  study  of  the  properties  of  solutions  led  to  the  discovery  of 
the  theory  of  electrolytic  dissociation,  it  was  soon  recognized  that  this 
theory  satisfied  the  conditions  quantitatively  only  for  very  dilute  solutions. 
The  laws  that  hold  for  the  properties  of  such  solutions  did  not  hold  for 
solutions  that  were  concentrated.  Indeed,  they  did  not  apply  to  solutions 
of  even  moderate  concentration;  not  to  those  solutions  with  which,  for  the 
most  part,  we  actually  have  to  deal  in  chemistry.  If  the  solutions  were 
fairly  concentrated,  the  laws  of  osmotic  pressure,  of  lowering  of  freezing- 
point,  and  lowering  of  vapor-tension  did  not  hold  at  all. 

Why  this  was  true  was  not  known.  It  was  simply  said  that  the  laws 
of  solutions  do  not  hold  for  concentrated  solutions,  just  as  the  laws  of  gases 
do  not  hold  for  concentrated  gases,  which,  of  course,  was  simply  an  analogy 
and  explained  nothing. 


GENERAL   DISCUSSION    OF   RESULTS.  143 

This  failure  of  the  gas  laws  to  apply  to  even  fairly  concentrated  solu- 
tions was  held  up  by  the  early  opponents  of  the  theory  of  electrolytic 
dissociation  as  a  weak  point  in  this  generalization  as  a  general  theory  of 
solutions,  and  it  must  be  confessed  with  some  justice.  We  had  here  a 
theory  of  solutions  which  applied  quantitatively  only  to  ideal  solutions, 
and  did  not  accord  with  the  facts  for  a  single  solution  of  even  moderate 
concentration.  Further,  there  was  no  reasonable  explanation  offered  to 
account  for  this  failure.  In  the  case  of  gases,  Van  der  Waal's  equation 
adapted  the  simpler  gas  laws  even  to  fairly  concentrated  gases,  but  in  the 
case  of  solutions  there  was  apparently  no  way  to  account  for  these  dis- 
crepancies between  the  facts  and  theory;  and  thus  the  matter  stood  for 
quite  a  time. 

The  theory  of  electrolytic  dissociation  said  simply  this,  that  when 
molecules  of  acids,  bases,  and  salts  are  brought  into  the  presence  of  water, 
they  are  broken  down  into  ions,  to  a  greater  or  less  extent  depending  upon 
the  concentration  of  the  solution.  It  did  not  recognize  any  combination 
of  the  solvent  with  the  dissolved  molecules  or  the  ions. 

The  dilution  of  the  solution  was  determined  by  the  amount  of  dis- 
solved substance  in  a  given  volume  of  the  solution,  assuming  that  all  of 
the  liquid  present  was  acting  as  solvent. 

We  now  know  that  this  is  not  the  case.  A  part  of  the  solvent  is,  in 
most  cases,  combined  with  the  dissolved  substance  and  is  not  playing  the 
role  of  solvent.  There  is,  therefore,  less  solvent  present  than  was  supposed, 
and  this  is  the  same  thing  as  to  say  that  the  solution  is  more  concentrated 
than  it  was  thought  to  be  from  the  way  in  which  it  was  prepared. 

The  amount  of  the  combined  solvent  may  be  small,  as  in  the  cases  where 
the  dissolved  substances  do  not  crystallize  with  any  of  the  solvent  of 
crystallization.  It  may,  however,  be  very  large,  as  in  the  case  of  aluminium 
chloride  in  water  at  what  is  supposed  to  be  twice  normal  concentration. 
Here  about  four-fifths  of  the  water  present  is  in  combination  with  the 
dissolved  substance,  and  the  solution  is  really  about  five  times  as  concen- 
trated as  would  be  supposed  from  the  amount  of  the  salt  present  in  a  given 
volume. 

We  thus  see  a  reason  for  the  failure  of  the  gas  laws  to  hold  for  con- 
centrated solutions.  In  dilute  solutions  the  amount  of  water  combined 
with  the  dissolved  substance,  as  compared  with  the  total  amount  of  water 
present,  is  practically  negligible.  In  more  concentrated  solutions,  however, 
the  amount  of  the  combined  water  may  be  a  very  appreciable  part  of  the 
total  water  present,  or  in  extreme  cases,  as  that  of  aluminium  chloride  cited 
above,  it  may  be  several  times  the  water  that  is  present  acting  as  solvent. 
Concentrated  solutions  are  thus  more  concentrated  than  we  would  suppose 
without  the  theory  of  solvation,  and  this  accounts  for  the  failure  of  the  gas 
laws  to  apply  to  such  solutions. 

A  theory  to  be  of  greatest  scientific  value  must,  of  course,  be  quanti- 
tative. While  we  have  not  been  able,  up  to  the  present,  to  determine 
accurately  the  magnitude  of  the  hydration  in  aqueous  solutions,  yet  the 
approximate  composition  of  the  hydrates  formed  by  a  large  number  of 
substances  at  various  concentrations  has  been  worked  out;  so  that  the 


144  A    STUDY   OF   THE   ABSORPTION    SPECTRA. 

theory  of  solvation,  as  far  as  aqueous  solutions  are  concerned,  is  now  on 
approximately  a  quantitative  basis. 

The  question  arises,  in  this  connection,  why  is  a  true  and  adequate 
theory  of  solutions  of  such  importance  not  only  for  physical  or  general 
chemistry,  but  for  so  many  branches  of  science?  The  answer  is  to  be  found 
in  the  importance  of  solutions,  in  the  broad  sense  of  that  term,  for  the 
natural  sciences.  The  one  reason  above  all  others  why  physical  chemistry 
has  reached  out  into  so  many  branches  of  science,  is  that  it  deals  scientifi- 
cally with  solutions.  Into  what  branch  of  science  do  solutions  not  enter? 
Chemistry  is  essentially  a  science  of  solutions.  Physics  depends  upon  solu- 
tions for  many  of  its  more  important  developments.  Geology  deals  with 
the  results  of  solution  not  only  in  the  sedimentary  rocks,  but  in  the  fused 
magmas.  We  might  almost  say  without  solution  no  geology. 

When  we  turn  to  the  biological  sciences  we  find  many  of  them  funda- 
mentally connected  with  the  science  of  solutions.  This  is  especially  true 
of  physiology,  as  Loeb  has  shown.  It  is  almost  equally  true  of  pharma- 
cology; and  solutions  are  of  fundamental  importance  for  physiological 
chemistry,  physiological  botany,  and  pathology.  Indeed,  about  the  only 
branch  of  natural  science  that  seems  to  be  independent  of  solutions  is 
astronomy. 

We  can  see  from  the  above  why  a  theory  that  accounts  for  the  prop- 
erties of  solutions  in  general  is  of  fundamental  importance  for  the  develop- 
ment of  the  natural  sciences. 

A  word  as  to  the  relation  between  the  solvate  theory  and  the  theory  of 
electrolytic  dissociation,  lest  some  one  should  suppose  that  they  are  antag- 
onistic. The  theory  of  electrolytic  dissociation,  as  has  been  pointed  out, 
simply  says  that  molecules  of  electrolytes  in  the  presence  of  a  dissociating 
solvent  are  broken  down  more  or  less  into  ions.  It  does  not  raise  any 
question  as  to  whether  the  ions  are  or  are  not  combined  with  any  of  the 
solvent.  It  has  been  shown  that  while  this  theory  is  necessary  to  account 
for  the  properties  of  solutions,  and  is  accepted  without  question  by  prac- 
tically all  chemists  of  reputation,  it  is  not  sufficient  to  account  for  the 
properties  especially  of  concentrated  solutions. 

We  must  go  farther  than  recognize  dissociation  and  determine  its 
magnitude.  We  must  find  out  the  condition  of  the  ions  in  solution  after 
they  are  formed,  and  of  the  undissociated  molecules.  This  the  theory  of 
solvation  aims  to  do.  It  attempts  to  answer  the  question  whether  the 
molecules  or  ions  are  combined  with  any  part  of  the  solvent,  and,  if  so, 
with  how  much.  The  theory  of  solvation  thus  supplements  the  theory 
of  ionization,  and  when  the  former  is  upon  as  good  a  quantitative  basis 
as  the  latter,  we  shall  have  a  satisfactory  theory  of  solution. 


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a  Number  of  Electrolytes  in  Aqueous  Solutions;  together  with  a  Brief,  General 
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683  (1907). 

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10  145 


146  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

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these  Solvents.  Proceed.  Amer.  Philosoph.  Soc.,  47,  276  (1908). 

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Solutions  as  Conditioned  by  Temperature,  Dilution,  and  Hydrolysis.  Amer. 
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(1909). 

(24)  JONES  AND  ANDERSON.    The  Absorption  Spectra  of  Solutions  of  a  Number  of  Salts 

in  Water,  in  Certain  Nonaqueous  Solvents,  and  in  Mixtures  of  These  Solvents 
with  Water.  Amer.  Chem.  Journ.,  41,  163  (1909). 

(25)  JONES  AND  STRONG.    The  Absorption  Spectra  of  Various  Potassium,  Uranyl,  Ura- 

nous,  and  Neodymium  Salts  in  Solution,  and  the  Effect  of  Temperature  on  the 
Absorption  Spectra  of  Certain  Colored  Salts  in  Solution.  Proceed.  Amer.  Philo- 
soph. Soc.,  48,  194  (1909). 

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Effect  of  Temperature  on  Such  Spectra.     Amer.  Chem.  Journ.,  43,  37  (1910). 

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10,  499  (1909). 

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Detecting  the  Presence  of  Intermediate  Compounds  in  Chemical  Reactions.  Amer. 
Chem.  Journ.,  43,  224  (1910). 

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pounds.    Phil.  Mag.,  566,  April  (1910). 

(30)  JONES.     Evidence  Obtained  in  this  Laboratory  during  the  Past  Twelve  Years  for  the 

Solvate  Theory  of  Solution.     Ztschr.  phys.  Chem.  (1910). 

Hydrates  in  Aqueous  Solution.  Evidence  for  the  Existence  of  Hydrates  in  Solution,  their 
Approximate  Composition,  and  Certain  Spectroscopic  Investigations  Bearing 
upon  the  Hydrate  Problem.  By  Harry  C.  Jones,  with  the  Assistance  of  F.  H. 
Getman,  H.  P.  Bassett,  L.  McMaster,  and  H.  S.  Uhler.  Carnegie  Institution 
of  Washington  Publication  No.  60  (1907). 

Conductivity  and  Viscosity  in  Mixed  Solvents.  A  Study  of  the  Conductivity  and  Viscosity 
of  Solutions  of  Certain  Electrolytes  in  Water,  Methyl  Alcohol,  Ethyl  Alcohol,  and 
Acetone;  and  in  Binary  Mixtures  of  These  Solvents.  By  Harry  C.  Jones  and  C. 
F.  Lindsay,  C.  G.  Carroll,  H.  P.  Bassett,  E.  C.  Bingham,  C.  A.  Rouiller,  L.  Mc- 
Master, W.  R.  Veazey.  Carnegie  Institution  of  Washington  Publication  No. 
80  (1907). 

The  Absorption  Spectra  of  Solutions  of  Certain  Salts  of  Cobalt,  Nickel,  Copper,  Iron, 
Chromium,  Neodymium,  Praseodymium,  and  Erbium  in  Water,  Methyl  Alcohol, 
Ethyl  Alcohol,  and  Acetone,  and  in  Mixtures  of  Water  with  the  Other  Solvents. 
By  Harry  C.  Jones  and  John  A.  Anderson.  Carnegie  Institution  of  Washington 
Publication  No.  110  (1909). 

A  Study  of  the  Absorption  Spectra  of  Solutions  of  Certain  Salts  of  Potassium,  Cobalt, 
Nickel,  Copper,  Chromium,  Erbium,  Praseodymium,  Neodymium,  and  Uranium, 
as  affected  by  Chemical  Agents  and  by  Temperature.  By  Harry  C.  Jones  and 
W.  W.  Strong.  Carnegie  Institution  of  Washington  Publication  No.  130. 


DESCRIPTION  OF  THE  PLATES. 

In  the  description  of  the  plates  there  is  usually  given  the  time  of  exposure  and 
the  quantity  of  current  flowing  through  the  Nernst  glower.  Almost  invariably  the 
amount  of  light  entering  any  solution  is  the  same  for  every  strip  on  any  spectrogram. 
For  different  spectrograms  the  amount  of  light  varies  according  to  the  opacity  of  the 
solution.  In  many  cases  where  the  solutions  absorbed  completely  in  the  ultra-violet, 
an  exposure  was  made  in  the  extreme  ultra-violet  only  to  the  spark;  the  solution  not 
being  in  the  path  of  the  beam  of  light.  These  spark  lines  were  used  as  wave-length 
references.  In  making  an  exposure  to  a  reference  line  the  film  holder  was  never  moved, 
so  that  there  was  no  possibility  of  shifts.  In  a  few  cases  there  are  streaks  running 
parallel  to  the  strips.  This  is  due  to  bubbles  or  some  other  obstacles  in  the  solution 
opaque  to  the  light.  Glycerol  solutions  present  many  difficulties  of  this  kind.  One 
of  these  is  the  inequalities  in  a  glycerol  solution  produced  by  heating.  One  way  of  mak- 
ing the  light  illumination  across  any  strip  more  uniform,  is  by  moving  the  solution  back 
and  forth  in  the  path  of  the  beam  of  light. 

PLATE     1.  A.  Potassium  Chromate.     Depth  of  cell  constant,   3  mm.     Concentrations, 

2,  1.5,  1,  0.66,  0.46,  0.33  and  0.25  normal. 
B.  Potassium  Chromate.     Depth  of  cell  constant,  3  mm.     Concentrations,  0.25, 

0.19,  0.12,  0.08,  0.06,  0.04,  and  0.031  normal. 
PLATE     2.  A.  Potassium  Chromate.     Depth  of   cell  constant,  3  mm.      Concentrations, 

0.031,  0.023,  0.0156,  0.0103,  0.0072,  0.0052,  and  0.004  normal. 
B.  Potassium  Chromate.     Depth  of  cell  constant,   3  mm.     Concentrations, 

0.004,  0.003,  0.002,  0.0013,  0.0009,  0.00065,  and  0.0005  normal. 

PLATE  3.  A.  Potassium  Chromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18, 
and  24  mm.  Concentrations,  2,  1.5,  1,  0.66,  0.46,  0.33,  and  0.25 
normal. 

B.  Potassium  Chromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.  Concentrations,  0.25,  0.19,  0.12,  0.08,  0.06,  0.04,  and  0.031 
normal. 

PLATE  4.  A.  Potassium  Chromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.  Concentrations,  0.031,  0.023,  0.0156,  0.0103,  0.0072,  0.0052, 
and  0.004  normal. 

B.  Potassium  Chromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.  Concentrations,  0.004,  0.003,  0.002,  0.0013,  0.0009,  0.00065, 
and  0.0005  normal. 

PLATE     5.  A.  Potassium  Dichromate,  Beer's  Law.     Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.     Concentrations,  0.33,  0.25,  0.16,  0.11,  0.077,  0.055,  and  0.042 
normal. 
B.  Potassium  Dichromate.    Depth  of  cell  constant,  3  mm.     Concentrations, 

0.33,  0.25,  0.16,  0.11,  0.077,  0.055,  and  0.042  normal. 
PLATE     6.  A.  Potassium  Dichromate.     Depth  of  cell  constant,  3  mm.     Concentrations, 

0.042,  0.031,  0.02,  0.014,  0.0096,  0.007,  and  0.0052  normal. 
B.  Potassium  Dichromate.     Depth  of  cell  constant,  3  mm.     Concentrations, 

0.005,  0.004,  0.0025,  0.0017,  0.0012,  0.009,  and  0.0006  normal. 

PLATE  7.  A.  Potassium  Dichromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.  Concentrations,  0.041,  0.031,  0.02,  0.014,  0.0096,  0.007,  and 
0.0052  normal. 

B.  Potassium  Dichromate,  Beer's  Law.  Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 
24  mm.  Concentrations,  0.005,  0.004,  0.0025,  0.0017,  0.0012,  0.009, 
and  0.0006  normal. 

147 


148  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

PLATE    8.  A.  Potassium  Ferrocyanide.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.5,  0.37,  0.25,  0.17,  0.12,  0.09,  and  0.063  normal. 
B.  Potassium  Ferrocyanide.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.06,  0.046,  0.032,  0.021,  0.015,  0.011,  and  0.008  normal. 
PLATE    9.  A.  Potassium  Ferrocyanide,  Beer's  Law.     Depth  of  cell,  3,  4,  6,  9,  13,  18, 

and    24    mm.    Concentrations,    0.5,  0.37,  0.25,  0.17,  0.12,  0.09,  and 

0.063  normal. 
B.  Potassium  Ferrocyanide,  Beer's  Law.    Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 

24  mm.    Concentrations,  0.06,  0.046,  0.032,  0.021,  0.015,  0.011,  and 

0.008  normal. 
PLATE  10.  A.  Potassium  Ferricyanide.    Depth  of  cell  constant,  3  mm.    Concentrations, 

1,  0.75,  0.5,  0.33,  0.23,  0.166,  and  0.125  normal. 
B.  Potassium  Ferricyanide.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.125,  0.094,  0.0625,  0.0425,  0.029,  0.0208,  and  0.0156  normal. 

PLATE  11.  .A.  Potassium   Ferricyanide.      Depth  of  cell  constant,   3  mm.      Concentra- 
tions,   0.0156,    0.0118,    0.0078,    0.0053,    0.0036,    0.0026,   and    0.0019 

normal. 

B.  Potassium  Ferricyanide.      Depth  of  cell  constant,   3   mm.      Concentra- 
tions,   0.0019,    0.0013,    0.001,    0.0066,    0.00045,    0.00032,   and   0.00024 

normal. 
PLATE  12.  A.  Potassium  Ferricyanide,  Beer's  Law.    Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 

24  mm.     Concentrations,    1,   0.75,   0.5,   0.33,   0.23,   0.166,   and  0.125 

normal. 
B.  Potassium  Ferricyanide,  Beer's  Law.     Depth  of  cell,  3,  4,  6,  9,  13,  18,  and 

24  mm.     Concentrations,  0.125,  0.094,  0.062,  0.042,  0.029,  0.021,  and 

0.0156  normal. 
PLATE   13.  A.  Cobalt  Chloride  in  Water.     2.37  normal  concentration.    1.3  mm.  depth  of 

cell.     Temperatures,  2°,  14°,  30°,  45°,  60°,  70°,  81°  C.    Length  of  ex- 
posure, 3  minutes. 
B.  Cobalt  Chloride.     0.315  normal  concentration.    10.4   mm.  depth  of  cell. 

Temperatures,  2°,  14°,  30°,  44°,  60°,  75°,  81°  C.     Length  of  exposure,  3 

minutes. 
PLATE  14.  A.  Cobalt    Chloride.     0.04   normal   concentration.     83   mm.   depth  of    cell. 

Temperatures,  14°,  30°,  44°,  58°,  72°,  80°  C.     Length  of  exposure,  4 

minutes. 

B.  Cobalt  Nitrate.     2.3  normal  concentration,  2  mm.  depth   of    cell.    Tem- 
peratures, 2°,  14°,  28°,  45°,  60°,  75°,  85°  C..   Length  of  exposure,  3 

minutes. 
PLATE  15.  A.  Cobalt  Chloride.    0.125  normal.     12  mm.  depth  of  cell.    Temperatures, 

5°,  20°,  38°,  52°,  64°,  and  83°  C.     Length  of  exposure,  4  minutes. 
B.  Cobalt  Nitrate.     0.29  normal.     3  mm.  depth  of  cell.     Temperatures,  13°, 

27°,  42°,  61°,  73°,  and  85°  C.     Length  of  exposure,  2  minutes. 
PLATE  16.  A.  Cobalt  Sulphate.     1.0  normal.     3  mm.  depth  of  cell.     Temperatures,  6°, 

19°,  36°,  49°,  64°,  and  80°  C.     Length  of  exposure,  2  minutes. 
B.  Nickel  Sulphate.    2.0  normal.     3  mm.  depth  of  cell.     Temperatures,  5°, 

19°,  32°,  47°,  61°,  72°,  and  81°  C.     Length  of  exposure,  2  minutes. 
PLATE  17.  A.  Cobalt   Acetate.     1.0  normal.     3  mm.  depth  of  cell.    Temperatures,  4°, 

18°,  32°,  50°,  64°,  80°  C.     Length  of  exposure,  2  minutes. 
B.  Cobalt  Acetate.    0.125  normal.    24  mm.  depth  of  cell.    Temperatures,  7°, 

27°,  47°,  61°,  73°,  and  81°  C.     Length  of  exposure,  2  minutes. 
PLATE  18.  A.  Cobalt  and  Calcium  Chlorides.     Cobalt  Chloride,  0.237  normal;   Calcium 

Chloride,  4.14  normal.     Temperatures,  2°,  15°,  30°,  42°,  58°,  75°,  86°  C. 

Length  of  exposure,  3  minutes.     3  mm.  depth  of  cell. 

B.  Cobalt  and  Aluminium  Chlorides.     Cobalt  Chloride,  0.221  normal;  Alumin- 
ium Chloride,  2.75  normal.    Temperatures,  - 1.0°,  12°,  32°,  45°,  60°,  72°, 

and  87°  C.     Length  of  exposure,  3  minutes. 


DESCRIPTION   OF   THE    PLATES.  149 

PLATE  19.  A.  Cobalt  and  Aluminium  Chlorides.  Cobalt  Chloride,  0.00316  normal; 
Aluminium  Chloride,  3.06  normal.  Depth  of  cell,  150  mm.  Tem- 
peratures, 3°,  18°,  41°,  55°,  68°,  and  85°  C.  Length  of  exposure,  2 
minutes. 

B.  Cobalt  and  Calcium  Chlorides.    Cobalt  Chloride,  0.00948  normal;  Calcium 
Chloride,  4.6  normal.     Depth  of  cell,  50  mm.     Temperatures,  1°,  20°, 
32°,  45°,  58°,  75°,  88°  C.     Length  of  exposure,  3  minutes. 
PLATE  20.  A.  Cobalt  Sulphocyanate.     2  normal.     1  mm.  depth  of  cell.     Temperatures, 

3°,  18°,  31°,  45°,  60°,  and  80°  C.    Length  of  exposure,  3  minutes. 
B.  Cobalt  Sulphocyanate.    0.25  normal.     8  mm.  depth  of  cell.     Tempera- 
tures, 6°,  20°,  33°,  47°,  59°,  73°,  and  80°  C.     Length  of  exposure,  2 
minutes. 
PLATE  21.  A.  Nickel  Chloride.    0.332  normal.    16  mm.  depth  of  cell.    2  minutes  exposure. 

Temperatures,  5°,  19°,  33°,  45°,  60°,  71°,  82°  C. 
B.  Nickel  Chloride.    2.66  normal.     2  mm.  depth  of  cell.     2  minutes  exposure. 

Temperatures,  5°,  18°,  30°,  44°,  57°,  75°,  85°  C. 
PLATE  22.  A.  Nickel  Acetate.     0.5  normal.     9  mm.  depth  of  cell.     2  minutes  exposure. 

Temperatures,  6°,  23°,  38°,  52°,  64°,  74°,  84°  C. 
B.  Nickel  Acetate.    0.5  normal.     3  mm.  depth  of  cell.     2  minutes  exposure. 

Temperatures,  5°,  20°,  33°,  46°,  60°,  71°,  81°  C. 
PLATE  23.  A.  Copper  Bromide.     2.06  normal.     1  mm.  depth  of  cell.    Length  of  exposure, 

2  minutes.     Temperatures,  6°,  17°,  30°,  45°,  71°  C. 
B.  Copper  Bromide.    0.25  normal.    8  mm.  depth  of  cell.    Length  of  exposure, 

2  minutes.    Temperatures,  6°,  17°,  31°,  46°,  59°,  71°,  85°  C. 
PLATE  24.  A.  Copper  Nitrate.    4.04  normal.     2  mm.  depth  of  cell.     Length  of  exposure, 

2  minutes.     Temperatures,  5°,  15°,  30°,  45°,  60°,  76°,  87°  C. 

B.  Copper  Nitrate.    0.505  normal.    16  mm.  depth  of  cell.    Length  of  exposure, 

3  minutes.     Temperatures,  1°,  15°,  30°,  45°,  60°,  75°,  82°  C. 

PLATE  25.  A.  Chromium   Nitrate.      0.754  normal.      3  mm.  depth  of  cell.     Length  of 
exposure,  2  minutes.     Temperatures,  7°,   18°,  32°,  46°,  59°,  73°,  and 
84°  C. 
B.  Copper  Nitrate.    4.04  normal.     3  mm.  depth  of  cell.     Length  of  exposure, 

3  minutes.     Temperatures,  4°,  16°,  33°,  46°,  59°,  71°,  82°  C. 
PLATE  26.  A.  Chromium  Nitrate.    0.754  normal.    3  mm.  depth  of  cell.    3  minutes  exposure. 

Temperatures,  5°,  17°,  32°,  45°,  60°,  71°,  81°  C. 

B.  Chromium  Nitrate.  0.094  normal.  24  mm.  depth  of  cell.  3  minutes  ex- 
posure. Temperatures,  7°,  17°,  33°,  44°,  59°,  69°  C. 

PLATE  27.  A.  Chromium  Chloride.  0.125  normal  Chromium  Chloride.  2.28  normal 
Aluminium  Chloride.  9  mm.  depth  of  cell.  Length  of  exposure,  4  min- 
utes. Temperatures,  6°,  19°,  36°,  51°,  66°,  81°  C. 

B.  Chromium  Chloride.  0.125  normal  Chromium  Chloride.  3.45  normal 
Calcium  Chloride.  9  mm.  depth  layer.  5  minutes  exposure.  Tempera- 
tures, 6°,  19°,  31°,  45°,  64°  C. 

PLATE  28.  A.  Chrome  Alum  KCr(SOJ2.     0.0083  normal.    9  mm.  depth  of  cell.    3  min- 
utes exposure.    Temperatures,  5°,  18°,  33°,  46°,  61°,  71°,  83°  C. 
B.  Chromium  Sulphate.    0.125  normal.    3  mm.  depth  of  cell.    4  minutes  ex- 
posure.    Temperatures,  5°,  20°,  37°,  51°,  66°,  82°  C. 
PLATE  29.  A.  Strip  1.  ErCl3  in  Glycerol.    Temperature  15°  C. 
Strip  2.  ErCl3  in  Glycerol.    Temperature  200°  C. 
Strip  3.  U(SO<),  in  Glycerol.    Temperature  15°  C. 
Strip  4.  11(80-4),  in  Glycerol.     Temperature  200°  C. 

J5.  Strip  1.  NdCl3  in  Glycerol.  Temperature  15°  C.  Concentration  0.02  normal. 
Strip  2.  NdCl,  in  Glycerol.  Temperature  200°  C.  Concentration  0.02  normal. 
Strip  3.  NdCl3  in  Glycerol.  Temperature  15°  C.  Concentration  0.15  normal. 
Strip  4.  NdCl3  in  Glycerol.  Temperature  200°  C.  Concentration  0.15  normal. 
Strip  5.  ErClj  in  Glycerol.  Temperature  15°  C. 
Strip  6.  ErCl3  in  Glycerol.  Temperature  200°  C. 


150  A    STUDY   OF   THE    ABSORPTION    SPECTRA. 

PLATE  30.  A.  Neodymium  Bromide  in  Water.     1.66  normal.     45.6  mm.  depth  of  cell. 

Temperatures,  6°,  20°,  33°,  47°,  62°,  73°,  and  82°  C. 

B.  Erbium  Chloride  in  Water.     0.94  normal.     48  mm.  depth  of  cell.     Tem- 
peratures, 7°,  17°,  29°,  46°,  60°,  70°,  80°  C. 

PLATE  31.  A.  Praseodymium  Chloride.  2.56  normal.  3  mm.  depth  of  cell.  Tempera- 
tures, 7°,  23°,  40°,  52°,  68°,  83°  C. 

B.  Praseodymium  Chloride.    0.043  normal.    196  mm.  depth  of  cell.    Tempera- 
tures, 7°,  20°,  36°,  51°,  66°,  81°  C. 

PLATE  32.  A.  Praseodymium  Nitrate.  2.6  normal.  46.5  mm.  depth  of  cell.  Tempera- 
tures, 6°,  19°,  47°,  70°,  90°  C. 

B.  Praseodymium  Chloride.     2.56  normal.     48  mm.  depth  of  cell.     Tempera- 
tures, 7°,  20°,  35°,  51°,  66°,  84°  C. 
PLATE  33.  A.  Praseodymium  Nitrate.     2.6  normal.     3  mm.  depth  of  cell.    Temperatures, 

6°,  16°,  34°,  46°,  58°,  70°,  82°  C. 
B.  Neodymium  Nitrate.     2.15  normal.     3  mm.  depth  of  cell.     Temperatures, 

4°,  17°,  29°,  43°,  58°,  71°,  84°  C. 

PLATE  34.  A.  Neodymium  Chloride  in  Glycerol.     Depth  of  cell  constant,  9  mm.    Con- 
centrations, 0.84,  0.63,  0.42,  0.28,  0.196,  and  0.105  normal. 
B.  Neodymium  Chloride  in  Glycerol.     Depth  of  cell  constant,  3  mm.    Con- 
centrations, 0.105,  0.143,  0.196,  0.28,  0.42,  0.63,  and  0.84  normal. 

PLATE  35.  A.  Neodymium  Chloride  in  Glycerol.  Test  for  Beer's  Law.  Depth  of  cell, 
3,  4,  6,  9,  13,  18,  24  mm.  Concentrations,  0.84,  0.63,  0.42,  0.28,  0.196, 
0.143,  and  0.105  normal. 

B.  Neodymium  Chloride  in  Glycerol.  Constant  depth  of  cell,  24  mm. 
Concentrations,  0.105,  0.143,  0.196,  0.28,  0.42,  0.63,  and  0.84 
normal. 

PLATE  36.  A.  Neodymium  Chloride  in  Glycerol  and  Water.  Depth  of  cell,  2.2  mm.  Con- 
centrations of  Neodymium  Chloride,  0.84,  0.80,  0.76,  0.67,  and  0.59 
normal.  Percentages  of  Water,  0,  5,  10,  20,  30,  60,  and  90. 
B.  Neodymium  Chloride  in  Glycerol  and  Water.  Depth  of  cell,  32.5  mm. 
Concentrations,  0.59,  0.67,  0.76,  0.80,  and  0.84  normal.  Percentages 
of  Water,  90,  60,  30,  20,  10,  5,  and  0. 

PLATE   37.  A.  Neodymium  Chloride  in  Water.    3.4  normal.     12  mm.  depth  of  cell.    Tem- 
peratures, 11°,  22°,  33°,  45°,  59°,  73°,  and  85°  C. 
B.  Neodymium  Chloride  in  Water.      0.17  normal.      196  mm.  depth  of  cell. 

Temperatures,  5°,  16°,  28°,  42°,  59°,  72°,  and  82°  C. 

PLATE  38.  A.  Neodymium  Chloride  in  Water.    3.4  normal.    43  mm.  depth  of  cell.    Tem- 
peratures, 6°,  21°,  36°,  47°,  60°,  77°,  and  83°  C. 
B.  Neodymium   Nitrate  in  Water.    2.96  normal.    38.5  mm.   depth  of  cell. 

Temperatures,  7°,  17.5°,  30°,  44.5°,  59°,  70°,  and  82°  C. 
PLATE  39.  A.  Neodymium  Bromide.    1.66  normal.     6  mm.  depth  of  cell.     Temperatures, 

4.5°,  20°,  36°,  50°,  68°,  and  83°  C. 

B.  Neodymium  Bromide.  0.055  normal.  197.4  mm.  depth  of  cell.  Temper- 
atures, 5.5°,  16.5°,  29°,  42.5°,  55°,  68°,  and  84°  C. 

PLATE  40.  A.  Neodymium  and  Calcium  Chlorides  in  Water.     2.05  normal  Neodymium 
Chloride  added  to  4.6  normal  Calcium  Chloride.    Temperatures,  6°,  17°, 
31°,  49°,  63°,  74°,  and  82°  C. 
B.  Neodymium  Nitrate  in  Water.     0.036  normal.     197  mm.  depth  of  cell. 

Temperatures,  9°,  22°,  42°,  56°,  69°,  78°  C. 

PLATE  41.  A.  Neodymium  Acetate  to  which  HNO3  is  added.     Depth  of  cell,  30  mm. 
Concentration  of  Neodymium  Acetate,  0.041  normal.   Concentrations  of 
HNO3,  0.117,  0.234,  0.585,  1.17,  4.09,  8.18,  and  16.36. 
B.  Neodymium  Acetate   in  Water.     Concentration  constant,   0.041   normal. 

Depth  of  cell,  1,  2,  3,  6,  14,  and  34  mm. 
PLATE  42.  A.  Neodymium  Chloride  in  Glycerol.    0.15  normal.     Temperatures,  20°,  60°, 

110°,  150°,  180°  C. 

B.  Neodymium  Nitrate  in  Concentrated  Nitric  Acid.  Concentration,  0.4 
normal.  Depth  of  cell,  0.2,  0.8,  2,  6,  16,  and  32  mm. 


DESCRIPTION  OF  THE  PLATES.  151 

PLATE  43.  A.  Neodymium  Chloride  in  Water  and  Ethyl  Alcohol.     Solution  contained  8 

per  cent  water. 
Strips  1,  2,  3,  4,  Beer's  Law.     Concentrations  of  NdCl3,  0.5,  0.3,  0.1,  and 

0.05  normal. 

Strips  5,  6,  7.    Concentration,  0.5  normal.    Depth  of  cell  changed. 
B.  Neodymium  Acetate  in  Water.  Strip  1  represents  the  Neodymium  Acetate 
solution  in  Water.     Succeeding  strips  show  the  effect  of  adding  more 
and  more  Hydrobromic  Acid. 

PLATE  44.  A.  Neodymium  Acetate   in   Water.   0.041   normal.    Strip   1,  pure   aqueous 

solution.     Strip  2,    the  same   to   which  one  drop   of   HC1   has   been 

added.   Succeeding  strips  represent  the  addition  of  more  and  more  HC1. 

B.  Mixtures  of  Neodymium  Acetate  and  Neodymium  Chloride  in  Water.    Strip 

1,  all  Neodymium  Acetate.     Strip  7,  all  Neodymium  Chloride. 

PLATE  45.  A.  Neodymium  Acetate  in  Water.  Depth  of  cell,  30  mm.  Concentration  of 
Acetate,  0.041  normal.  Concentration  of  Hydrochloric  Acid,  0.113,  0.226, 
0.566,  1.13,  3.95,  7.91,  and  15.82. 

B.  Neodymium  Citrate  in  Water.  Depth  of  cell,  30  mm.  Strip  2  and  succeed- 
ing strips  show  the  effect  of  the  addition  of  HC1. 

PLATE  46.  A.  Strip  1.  0.15  normal  NdCl3  and  A1C13  in  Glycerol  at  10°  C. 
Strip  2.  Same  at  200°  C. 

Strip  3.  0.15  normal  NdCl3  and  CaCL,  in  Glycerol  at  10°  C. 
Strip  4.  Same  at  200°  C. 

Strip  5.  Uranous  and  Aluminium  Chlorides  in  Water  at  10°  C. 
Strip  6.  Same  at  100^  C. 

B.  Neodymium  Acetate  in  Water.     0.041  normal.     9  mm.  depth  of  cell.     Con- 
centrations of  HNO3,  0.117,  0.234,  0.585,  1.17,  4.09,  8.18,  and  16.36 
normal.     The  reaction  took  place  between  the  second  and  third  strips 
in  this  case. 
PLATE  47.  A.  Strip  1.  Neodymium  Chloride  in  Water. 

Strip  2.  Same  solution  to  which  about  ten  times  its  volume  of  strong  HC1 

has  been  added. 

Strip  3.  Neodymium  Chloride  in  HC1  at  10°  C. 
Strip  4.  The  same  at  100°  C. 
Strip  5.  Uranous  Acetate  at  10°  C. 
Strip  6.  The  same  at  100°  C. 

B.  Strip  1.  Uranyl  Nitrate  in  Strong  Nitric  Acid  at  10°  C. 
Strip  2.  The  same  at  100°  C. 
Strip  3.  The  same  at  10°  C. 

Strip  4.  Neodymium  Nitrate  in  Nitric  Acid  at  10°  C. 
Strip  5.  The  same  at  about  90°  C. 
Strip  6.  Neodymium  Chloride  in  Water. 

PLATE  48.  A.  Uranyl  Chloride  in  Water.     Beer's  Law.     Concentrations,  0.12,  0.16,  0.2, 
0.33,  0.5,  0.75,  and  1.0  normal.     Depths  of  cell,  24,  18,  13,  9,  6,  4, 
and  3  mm. 
B.  Uranyl  Chloride  in  Water.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.12,  0.16,  0.2,  0.33,  0.5,  0.75,  and  1.0  normal. 

PLATE  49.  A.  Uranyl  Chloride  in  Water.  Concentration  constant,  0.2  normal.  Depth 
of  cell,  3,  6,  12,  24,  and  35  mm.  This  plate  is  to  show  how  much  weaker 
the  uranyl  bands  are  in  a  pure  aqueous  solution,  compared  with  a  solu- 
tion containing  some  other  salt  or  hydrochloric  acid. 

B.  Uranyl  and  Aluminium  Chlorides  in  Water.  Concentration  Uranyl  Chloride, 
0.2  normal,  Aluminium  Chloride,  2.43  normal.  Depths  of  cell,  3,  6,  12, 
24,  and  35  mm. 

PLATE  50.  A.  Uranyl  and  Zinc  Chlorides  in  Water.  Concentration  Uranyl  Chloride,  0.2 
normal.  Zinc  Chloride  almost  saturated.  Depths  of  cell,  3,  6,  12,  24, 
and  35  mm. 

B.  Uranyl  Chloride  and  Hydrochloric  Acid.  Concentration  Uranyl  Chloride, 
0.2  normal;  Hydrochloric  Acid  very  strong.  Depth  of  cell,  3,  6,  12,  24, 
and  35  mm. 


152  A    STUDY    OF   THE   ABSORPTION    SPECTRA. 

PLATE  51.  A.  Uranyl  and  Aluminium  Chlorides  in  Water.  Depth  of  cell  constant,  6  mm. 
Concentration  of  Uranyl  Chloride  constant  at  0.25  normal.  Concentra- 
tions of  Aluminium  Chloride,  2.02,  1.61,  1.21,  0.81,  0.4,  and  0. 
B.  Uranyl  and  Aluminium  Chlorides  in  Water.  Depth  of  cell  constant,  3  mm. 
Concentration  of  Uranyl  Chloride  constant  at  0.25  normal.  Concentra- 
tions of  Aluminium  Chloride,  2.02,  1.61,  1.21,  0.81,  0.4,  and  0. 

PLATE  52.  A.  Uranyl  and  Calcium  Chlorides  in  Water.  Depth  of  cell  constant,  13  mm. 
Concentration  of  Uranyl  Chloride  constant  at  0.25  normal.  Concentra- 
tions of  Calcium  Chloride. 

B.  Uranyl  and  Calcium  Chlorides  in  Water.  Depth  of  cell  constant,  3  mm. 
Concentration  of  Uranyl  Chloride  constant  at  0.25  normal.  Concentra- 
tions of  Calcium  Chloride. 

PLATE  53.  A.  Uranyl  Chloride  in  Methyl  Alcohol.  Beer's  Law.  Depths  of  cell,  24,  19, 
15,  12,  9.5,  7.5,  and  6  mm.  Concentrations,  0.0625,  0.079,  0.10,  0.125, 
0.158,  0.20,  and  0.25  normal. 

B.  Uranyl  Chloride  in  Methyl  Alcohol.  Depth  of  cell  constant,  6  mm. 
Concentrations  0.0625,  0.079,  0.10,  0.125,  0.158,  0.20,  and  0.25 
normal. 

PLATE  54.  A.  Uranyl  and  Calcium  Chlorides  in  Methyl  Alcohol.  Concentration  Uranyl 
Chloride,  0.125  normal.  Depth  of  cell,  6  mm.  Concentrations  of 
Calcium  Chloride,  0.0,  0.144,  0.29,  0.43,  0.57,  0.72,  and  0.9  normal. 
B.  Uranyl  and  Calcium  Chlorides  in  Methyl  Alcohol.  Concentration  of  Uranyl 
Chloride,  0.125  normal.  Depth  of  cell,  3  mm.  Concentrations  of  Calcium 
Chloride,  0.0,  0.144,  0.29,  0.43,  0.57,  0.72,  and  0.9  normal. 

PLATE  55.  A.  Uranyl  Chloride  in  Methyl  Alcohol.    Depth  of  cell,  15mm.     Concentra- 
tions, 0.0625,  0.079,  0.10,  0.125,  0.158,  0.20,  and  0.25  normal. 
B.  Uranyl  Nitrate  in  Methyl  Alcohol.     Depth  of  cell  constant,  15  mm.    Con- 
centrations, 0.05,  0.063,  0.079,  1.0,  1.24,  1.58,  0.2  normal. 

PLATE  56.  Uranyl  Chloride  in  Methyl  Alcohol  and  Water.  Concentration  of  Uranyl 
Chloride,  0.1  normal.  Percentages  of  Water,  100,  50,  40,  32,  24,  16, 
and  8. 

A.  Depth  of  cell,  16.7  mm. 

B.  Depth  of  cell,  6  mm. 

PLATE  57.  A.  Uranyl  Chloride  in  Ethyl  Alcohol.  Depth  of  cell  constant,  15  mm.  Con- 
centrations of  Uranyl  Chloride,  0.0625,  0.079,  0.1,  0.125,  0.158,  0.2, 
and  0.25  normal. 

B.  Uranyl  Chloride  in  Methyl  Alcohol  and  Water.  Depth  of  cell  constant, 
6  mm.  Concentration  of  Uranyl  Chloride  constant.  Percentages  of 
Water,  100,  50,  40,  32,  24,  16,  and  8. 

PLATE  58.  A.  Uranyl  Chloride  in  Ethyl  Alcohol.  Concentrations,  0.0625,  0.079,  0.1, 
0.125,  0.158,  0.2,  and  0.25  normal.  Depths  of  cell,  24,  19,  15,  12,  9.5, 
7.5,  and  6  mm. 

B.  Uranyl  Chloride  in  Ethyl  Alcohol.  Depth  of  cell  constant,  6  mm. 
Concentrations,  0.0625,  0.079,  0.1,  0.125,  0.158,  0.2,  and  0.25 
normal. 

PLATE  59.  A.  Uranyl  Chloride  in  Glycerol.    Depth  of  cell  constant,  10  mm.     Concentra- 
tions, 0.176,  0.132,  0.088,  0.059,  0.041,  0.030,  and  0.022  normal. 
B.  Uranyl  Chloride  in  Glycerol.    Depth  of  cell  constant,  5  mm.    Concentra- 
tions, 0.176,  0.132,  0.088,  0.059,  0.041,  0.030,  and  0.022  normal. 

PLATE  60.  Uranyl  Chloride  in  Mixtures  of  Glycerol  and  Methyl  Alcohol.  Concentration 
of  Uranyl  Chloride  constant,  0.176  normal.  Percentages  of  Methyl 
Alcohol,  0,  15,  30,  45,  60,  75,  and  90. 

A.  Depth  of  cell,  25  mm. 

B.  Depth  of  cell,  3  mm. 

PLATE  61.  A.  Uranyl  Chloride  in  Water.    Concentration  1.0  normal.      Depth  of   cell, 

3  mm.     Temperatures,  6°,  18°,  34°,  52°,  68°,  and  82°  C. 

B.  Uranyl  Chloride  in  Water.  Concentration,  £  normal.  Depth  of  cell,  196  mm. 
Temperatures,  6°,  18°,  29°,  44°,  59°,  71°,  and  81°  C. 


DESCRIPTION   OF   THE    PLATES.  153 

PLATE  62.  A.  Uranyl  Nitrate  in  Water.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.19,  0.25,  0.37,  0.5,  0.75,  1.12,  and  1.5  normal. 

B.  Uranyl  Nitrate  in  Water.  Concentration  constant,  0.022  normal.  Depth 
of  cell,  3,  4,  6,  9,  12,  18,  and  24  mm.  Since  Beer's  law  holds  this  is 
equivalent  to  keeping  the  depth  of  cell  constant  and  changing  the 
concentration. 

PLATE  63.  A.  Uranyl  Nitrate  in  Water.     Concentrations,  0.187,  0.25,  0.375,  0.5,  0.75, 
1.125,  and  1.5  normal.     Depth  of  cell  for  red,  15  mm.;  for  the  ultra- 
violet, 3  mm. 
B.  Uranous  Chloride  in  Water.    Depth  of  cell,  2  mm.    Temperatures,  S°,  17°, 

33°,  48°,  62°,  73°,  and  80°  C. 

PLATE  64.  A.  Uranyl  Nitrate  in  Water.  Beer's  Law.  Depth  of  cell,  24,  18,  13,  9,  6,  4, 
3  mm.  Concentrations,  0.187,  0.25,  0.375,  0.5,  0.75,  1.125,  and  1.5 
normal. 

B.  Uranyl  Nitrate  in  Water.  Depth  of  cell,  24,  18, 13,  9,  6,  4,  and  3  mm.  Con- 
centrations, 0.0234,  0.0312,  0.047,  0.0625,  0.094,  0.14,  and  0.1875 
normal. 

PLATE  65.  A.  Strip  1.  Uranyl  Nitrate  in  Water.    1.1  normal.    Depth  of  layer,  3  mm. 
Strip  2.  Is  identical  with  strip  1. 

Strip  3.  Water  is  added  so  as  to  make  the  depth  of  cell  380  mm. 
Strip  4.  Uranyl  Sulphate.    0.75  normal.     Depth  of  layer,  4  mm. 
Strip  5.  Water  is  added  so  as  to  make  the  depth  of  cell  380  mm. 
Strip  6.  Uranyl  Acetate.     0.188  normal  solution. 
Strip  7.  Water  is  added  so  as  to  make  the  depth  of  cell  380  mm. 
B.  Strip  1.  Uranyl  Sulphate  in  Water.     1.0  normal.    Depth  of  layer,  3  mm. 
Strip  2.  Uranyl  Acetate  in  Water.    0.25  normal.    Depth  of  layer,  12  mm. 
Strip  3.  Uranyl  Nitrate  in  Water.     0.75  normal.     Depth  of  layer,  4  mm. 
Strip  4.  Uranyl  Sulphate  in  Water.    0.75  normal.    Depth  of  layer,  4  mm. 
PLATE  66.  Uranyl   Nitrate   in   Methyl   Alcohol    and   Water.     Concentration   of  Uranyl 
Nitrate  constant  at  0.1  normal.     Percentages  of  Water,  50,  40,  32,  24, 
16,  8,  and  0. 

A.  Depth  of  cell,  15  mm. 

B.  Depth  of  cell,  6  mm. 

PLATE  67.  A.  Uranyl  Nitrate  in  Methyl  Alcohol,  Beer's  Law.  Depth  of  cell,  6,  7.5,  9.5, 
12,  15,  19,  and  24  mm.  Concentrations,  0.2,  0.16,  0.127,  0.10,  0.08, 
0.063,  and  0.033  normal. 

B.  Uranyl  Nitrate  in  Methyl  Alcohol.    Depth  of  cell  constant,  3  mm.    Con- 
centrations,   0.05,  0.063,  0.079,  0.10,  0.124,  0.158,  and  0.2  normal. 
PLATE  68.  A.  Uranyl  Nitrate  in  Ethyl  Alcohol.    Beer's  Law.    Depth  of  cell,  6,  7.5,  9.5, 
12,  15,  19,  and  24  mm.     Concentrations,  0.2,  0.16,  0.127,  0.10,  0.08, 
0.063,  and  0.033  normal. 

B.  Depth  of  cell  constant,  15  mm.    Concentrations,  0.033,  0.063,  0.08,  0.10, 

0.127,  0.16,  and  0.2  normal. 
PLATE  69.  Strip  1.  Uranyl  Nitrate  in  Glycerol. 

Strip  2.  Uranyl  Nitrate  in  three  parts  of  Glycerol  to  one  of  Water. 

Strip  3.  Uranyl  Nitrate  in  two  parts  of  Glycerol  to  two  of  Water. 

Strip  4.  Uranyl  Nitrate  in  one  part  of  Glycerol  to  three  of  Water. 

Strip  5.  Uranyl  Nitrate  in  one  part  of  Glycerol  to  three  of  Acetone. 

Strip  6.  Uranyl  Nitrate  in  one  part  of  Glycerol  to  three  of  Alcohol. 

A.  Depth  of  cell,  25  mm. 

B.  Depth  of  cell,  6  mm. 

PLATE  70.  A.  This  Spectrogram  gives  the  Absorption  Spectra  of  a  solution  of  Uranous 
Chloride  in  Hydrochloric  Acid  to  which  Acetone  was  added  to  increase 
the  cell  depth.    Depth  of  cell,  5,  6,  8,  10,  15,  and  30  mm. 
B.  Uranyl  Nitrate  in  Nitric  Acid.    0.12  normal.    Depth  of  cell,  1.2,  2,  3,  4,  6, 
11,  and  24  mm. 


154 


A    STUDY    OF   THE    ABSORPTION    SPECTRA. 


PLATE  71.  A.  Uranyl  Nitrate  in  Water.     ^  normal.    Depth  of  cell,  196  mm.    Tempera- 
tures, 9.5°,  23°,  46°,  59°,  70°,  and  79°  C. 

B.  Uranyl  Nitrate  in  Water.    1.0  normal.     Depth  of  cell,  3  mm.    Tempera- 
tures,  11°,  24.5°,  40°,  53.5°,  67.5°,  and  82°  C. 

PLATE  72.  A.  Uranyl  Bromide  in  Water,  Beer's  Law.     Depth  of  cell,  24,  18,  12,  9,  6, 
4,  and  3  mm.     Concentrations,  0.16,  0.2,  0.25,  0.33,  0.5,  0.75,  and  1.0 
normal. 
B.  Uranyl  Bromide  in  Water.    Depth  of  cell  constant,  3  mm.    Concentrations, 

0.16,  0.2,  0.25,  0.33,  0.5,  0.75,  and  1.0  normal. 

PLATE  73.  A.  Uranyl  Sulphate  in  Water.     1.0  normal.    Depth  of  cell,  3  mm.    Tempera- 
tures, 5°,  19°,  32°,  54°,  67°,  and  84°  C. 

B.  Uranyl  Sulphate  in  Water.    0.0156  normal.    Depth  of  cell,  196  mm.    Tem- 
peratures, 6°,  19°,  36°,  51°,  67°,  and  81°  C. 

PLATE  74.  A.  Uranyl  Acetate  in  Water,   Beer's  Law.     Depth   of  cell,  24,  18,  12,  9,  6, 
4  and  3  mm.     Concentrations,  0.031,  0.042,  0.062,  0.083,  0.125,  0.18, 
and  0.25  normal. 
B.  Uranyl  Acetate  in  Water.    Concentration  constant,  0.031  normal.     Depth 

of  cell,  3,  4,  6,  9,  12,  18,  and  24  mm. 

PLATE  75.  A.  Uranyl  Acetate  in  Methyl   Alcohol,  Beer's  Law.     Concentrations,  0.06, 
0.07,   0.10,    0.12,    0.16,   0.20,  and   0.25  normal.     Depth  of  cell,   24, 
19,  15,  12,  9.5,  7.5,  and  6  mm. 
B.  Depth  of  cell  constant,   6  mm.      Concentrations,   0.06,  0.07,  0.10,  0.12, 

0.16,  0.20,  and  0.25  normal. 
PLATE  76.  A.  Uranyl  Chloride  in  Water.    Concentration,  1.0  normal.    Depth  of  cell,  1,  2, 

4,  18,  16,  32,  and  45  mm. 

B.  Uranyl  Acetate  in  Water.     0.25  normal.    Depth  of  cell,  3  mm.    Tempera- 
tures, 5°,  19°,  32.5°,  47.5°,  61°,  70.5°,  and  84°  C. 

77.  Uranyl  Nitrate  in  Water. 

A.  Effect  of  adding  Acetic  Acid  on  the  Uranyl  Nitrate  bands. 

B.  Effect  of  adding  Hydrochloric  Acid  on  the  Uranyl  Nitrate  bands. 

78.  A.  Uranous  Bromide  in  Methyl  Alcohol.     Depth  of  cell,  3,  6,  11,  and  16  mm. 

B.  Uranyl  Nitrate  in  Water  to  which  Hydrobromic  Acid  is  added. 

C.  Mixtures  of  Uranyl  Nitrate  and  Uranyl  Sulphate  in  Water. 


PLATE 
PLATE 


Strip  1. 

Strip  2. 

Strip  3. 

Strip  4. 

Strip  5. 

Strip  6. 

Uranyl  Nitrate  .  . 

Pet. 
100 
0 

Pet. 
80 
20 

Pet. 
60 
40 

Pet. 
40 
60 

Pet. 
20 
80 

Pet. 
0 
100 

Uranyl  Sulphate  

PLATE  79.  A.  Uranyl  Acetate  in  Water.  Depth  of  cell,  10  mm.  Concentration  of  Uranyl 
Salt,  0.05  normal.  Concentration  Nitric  Acid,  0.0028,  0.0056,  0.0140, 
0.028,  0.140,  0.28,  and  0.56  normal. 

B.  Uranyl  Nitrate  in  Water  to  which  Hydrochloric  Acid  is  added. 
PLATE  80.  A.  Uranous  Acetate  in  Water  to  which  Nitric  Acid  is  added. 

B.  The  first  four  strips  give  the  effect  of  adding  Hydrochloric  Acid  to  a  Nitric 
Acid  solution  of  Uranyl  Nitrate.  The  remaining  strips  represent  the 
same  effect  obtained  by  using  a  greater  depth  of  cell. 

PLATE  81.  A.  Uranous  and  Aluminium  Chlorides  in  Water  to  which  Nitric  Acid  is  added. 
B.  Uranyl  Nitrate  in  Water  to  which  Sulphuric  Acid  is  added.     Depth  of  cell 
15  mm.     Concentration  of  Uranyl  Salt,  0.04  normal.     Percentage  of 
acid,  1.84,  3.68,  7.36,  14.72,  29.44,  58.88,  and  88.32. 
PLATE  82.  A.  Uranyl  Nitrate  to  which  Acetic  Acid  is  added. 

B.  Uranyl  Nitrate  in  Water  to  which  Sulphuric  Acid  is  added.     Depth  of  cell 

8  mm.;  otherwise  this  is  the  same  as  B,  Plate  81. 

PLATE  83.  A.  Uranyl  Nitrate  in  Water  to  which  Sulphuric  Acid  is  added. 
B.  Uranyl  Nitrate  in  Water  to  which  Acetic  Acid  is  added. 


DESCRIPTION   OP   THE    PLATES.  155 

PLATE  84.  A.  Uranous  Chloride  in  Water.    Concentration  constant.    Depth  of  cell,  1.2' 

2,  4,  8,  16,  and  32  mm. 

B.  Uranous  and  Aluminium  Chlorides  in  Water.     Depth  of  cell,  1.2,  2,  4,  8, 

16,  and  32  mm. 

PLATE  85.  A.  This  spectrogram  shows  the  absorption  of  Uranous  Chloride  in  Acetone  to 
which  more  and  more  Water  is  added.    The  "Water  "  and  "Acetone  " 
bands  appear  on  this  plate. 
B.  This  spectrogram  shows  the  same  process,  a  more  concentrated  solution  of 

Uranous  Chloride  in  Acetone  being  used  in  this  case. 

PLATE  86.  A.  Uranous  Chloride  in  Glycerol  and  mixtures  of  Glycerol  and  Water.    The  first 

strip  represents  the  absorption  of  a  6  mm.  solution  of  Uranous  Chloride 

in  Glycerol.    Succeeding  strips  show  the  effect  of  the  addition  of  Water. 

B.  This  is  exactly  similar  to  A  except  that  Methyl  Alcohol  was  added  instead 

of  Water. 
PLATE  87.  A.  Uranous  Chloride  in  Methyl  Alcohol.     Concentration  constant. 

B.  Uranous  Acetate  in  Methyl  Alcohol.   Concentration  constant. 

C.  Uranous  Chloride  in  Glycerol.     Concentration   constant.     Depth  of  cell, 

3,  4,  6,  9,  13,  18,  and  24  mm. 

PLATE  88.  A.  Uranous  Chloride  in  Ethyl  Alcohol.     Concentration  constant.     Depth  of 

cell,  3,  6,  12,  24,  and  35  mm. 
B.  Uranous  Chloride  in   Methyl  Alcohol.     Concentration    constant.     Depth 

of  cell,  3,  6,  12,  24,  and  35  mm. 
PLATE  89.  A.  Uranyl  Chloride  in  Methyl  Alcohol  to  which  Water  is  added. 

B.  Uranous  Chloride  in  Methyl  Alcohol.     Concentration  constant. 

PLATE  90.  A.  Uranous  Chloride  in  Acetone.  Depths  of  cell,  5,  6,  8.3,  and  15  mm.  The 
first  strip  represents  Uranous  Chloride  in  Acetone,  and  the  following 
strips  represent  the  same  to  which  Hydrochloric  Acid  had  been  added. 

B.  In  this  case  Uranyl  Chloride  instead  of  Uranous  Chloride  was  used.    Depth 

of  cell,  2,  3.4,  4,  5,  11,  and  30  mm. 

C.  Strips  1,  2,  and  3  represent  the  same  effect  as  A. 

Strip  4  represents  an  Ether  solution  of  Uranous  Chloride. 
Strips  5,  6,  and  7  the  absorption  of  2,  5,  and  14  mm.,  respectively,  of  Ura- 
nous Chloride  in  Acetone. 
PLATE  91.  A.  Uranous  Bromide  in  Methyl  Alcohol. 

B.  Uranous  Acetate  in  Water  to  which  more  and  more  Nitric  Acid  is  added. 
PLATE  92.  A.  Uranous  Bromide  in  Water,  Beer's  law  test.     The  original  solution  con- 
sisted of  an  0.8  mm.  layer.    To  this  was  added  Water  so  as  to  make  the 
depth  of  solution  2.8,  6,  12.5,  22,  and  35  mm. 
B.  Uranous  Bromide  in  Glycerol.    0.06  normal  Concentration.     Depth  of  cell, 

5,  7.5,  10,  15,  20,  26,  and  33  mm. 
PLATE  93.  A.  Uranyl  Nitrate  in  Nitric  Acid  to  which  Sulphuric  Acid  is  added.     Depth 

of  cell,  8,  8.4,  9,  12,  and  17  mm. 
B.  Uranous   Acetate  in   Acetic  Acid  to  which  Hydrobromic  Acid  is  added. 

Depth  of  cell,  22,  22.3,  24,  30,  and  36  mm. 
PLATE  94.  A.  An  Acid  Solution  of  Uranous  Chloride  to  which  Ethyl  Alcohol  is  added. 

Depth  of  cell  being  4.5,  5,  7,  15,  and  35  mm. 
B.  Uranous  Chloride  in  Water  to  which  Acetic  Acid  is  added.     Depth  of  cell, 

5,  5.8,  7.5,  and  26  mm. 
PLATE  95.  A.  Uranous  Chloride  in  Acetone.     Depth  of  cell  varied. 

B.  Uranous  Chloride  in  Methyl  Alcohol.     Depth  of  cell,  2.4,  6,  8,  and  12  mm. 

C.  Uranous  Chloride  in  Glycerol.    Depth  of  cell,  2,  4,  6,  8,  12,  and  24  mm. 
PLATE  96.  A.  Uranous  Chloride  in  Water  to  which  Ethyl  Alcohol  is  added.    Depth  of 

cell,  3.2,  4.4,  6.4,  12,  and  22.5  mm. 

B.  Uranous  Acetate  in  Water.     Depth  of  cell,  3,  6,  12,  24,  and  35  mm. 

C.  Uranyl  Acetate  in  Acetone  and  Acetic  Acid.     Depth  of  cell  3,  6,  12,  24, 

and  35  mm. 


156  A    STUDY    OF   THE    ABSORPTION    SPECTRA. 

PLATE  97.  A.  Uranous  Acetate  in  Water  to  which  Nitric  Acid  is  added. 

B.  Uranyl  Nitrate  in  Strong  Nitric  Acid.     Strip  1,  1.2  mm.  of  solution  then  2, 

3,  5,  and  12  (4  mm.)  drops  of  Hydrochloric  Acid  was  added.   The  last 

strip  shows  the  absorption  of  9.5  mm.  of  the  solution. 
PLATE  98.  A.  Uranous  Chloride  to  which  a  concentrated  solution  of  Aluminium  Chloride 

is  added.     Strip  1,  3  mm.  of  Uranous  Chloride  solution  plus  1  mm. 

A1C13;   strip  2,  the  same  to  which  2  mm.  of  A1C13  solution  is  added; 

strip  3,  to  which  10  mm.  more  of  A1C13  is  added;  strip  4  is  a  3  mm. 

solution  of  Uranous  Chloride,  and  strip  5  is  the  same  to  which  13  mm. 

HC1  has  been  added. 
B.  (1)  Uranous  Chloride  in  Water,  4  mm.;  (2)  plus  Methyl  Alcohol  to  6.3  mm.; 

(3)  plus  Methyl  Alcohol  to  7.5  mm.;  (4)  Uranous  Chloride  in  Water, 

4  mm.;  (5)  the  same  plus  Acetic  Acid  to  28  mm.;  (6)  4  mm.  of  Uranous 

Chloride  in  Water  plus  2  mm.  HNO3;    (7)  4  mm.  Uranous  Chloride  in 

Water  plus  19  mm.  HjSO4. 


INDEX. 


Absorption  and  emission  spectra,  meth- 
ods of  studying 16 

spectra    of    anhydrous    ur- 
anyl chloride 99 

of  erbium  nitrate  and 
other  salts  of  erb- 
ium   64 

of  uranium  com- 
pounds   85 

of  uranyl  chloride . .  89 

organic 10 

Acetate  of  chromium 54 

of  cobalt 38 

of  nickel 44 

Alum,  chrome 54 

Aluminium  and    uranous    chlorides    in 

water 123 

chloride  and  chromium  chlo- 
ride    52 

and  cobalt  chloride .   39 
Anderson's  method    for    studying    the 
effect  of  temperature   on  absorption 

spectra 20 

Anhydrous  uranyl  acetate Ill 

chloride,     absorption 

spectra  of 99 

nitrate,  absorption  of,  107 

Aqueous  solutions  of  cobalt  salts 34 

Atomic  structure  and  spectra 9 


Banded  spectra 7 

Bibliography 145 

Bromide  of  copper 47 


Calcium  chloride  and  chromium  chloride  52 

and  cobalt  chloride.. . .   38 

Chemical  analysis,  spectrum  method  of.     8 

Chloride  of  chromium 51 

of  nickel 43 

of  praseodymium 65 

of  uranyl 88 

Chromate  potassium 25 

Chrome  alum 54 

Chromium  acetate 54 

chloride 51 

and  aluminium  chlo- 
ride...   52 

and  calcium  chloride  52 
in  water — conductiv- 
ity and  tempera- 
ture coefficients. .  55 

nitrate 63 

in  water — conductiv- 
ity and  tempera- 
ture coefficients —  55 

salts 49 

sulphate 53 

Chromophores,  theory  of 11 


Cobalt  acetate 38 

bromide  in  water — conductivity 

and  dissociation. 41 

chloride  and  aluminium  chloride  39 

and  calcium  chloride 38 

in    water — conductivity 

and  dissociation 41 

nitrate 37 

in    water — conductivity 

and  dissociation 41 

salts 31 

in  glycerol 34 

in  water 34 

sulphate 38 

sulphocyanate 40 

Complexity  of  spectrum  problem 13 

Conductivity  and  dissociation  of  cobalt 

bromide  in  water 41 

and  dissociation  of  cobalt 

chloride  in  water 41 

and  dissociation  of  cobalt 

nitrate  in  water ....  41 

and  dissociation  of  nickel 

chloride  in  water 45 

and  dissociation  of  nickel 

nitrate  in  water 45 

and  temperature  coeffi- 
cients of  chromium  chlo- 
ride in  water 55 

and  temperature  coeffi- 
cients of  chromium  ni- 
trate in  water 55 

and  temperature  coeffi- 
cients of  uranyl  acetate 

in  water 116 

and  temperature  coeffi- 
cients of  uranyl  chloride 

in  water 115 

and  temperature  coeffi- 
cients of  uranyl  nitrate 

in  water 115 

Copper  bromide 47 

nitrate 47 

salts...  ..  47 


Description  of  the  plates 147 

Bichromate  potassium 26 

Discussion  of  results 137 

Dynamic  isomerism,  theory  of 12 

Emission  and  absorption  spectra,  meth- 
ods of  studying 16 

Erbium  chlonde  in  glycerol 63 

in  water — effect  of  tem- 
perature   63 

nitrate  and  other  salts  of  erbi- 
um, absorption  spectra  of 64 

salts.......    ....    . 57 

Experimental  methods  used 19 

157 


158 


INDEX. 


Ferricyanide  of  potassium  in  water 28 

Ferrocyanide  of  potassium  in  water 27 

Fluorescent  and  phosphorescent  spectra 

of  uranyl  salts 116 

Foreign  salts,  effect  of  the  presence  of, 

on  absorption  spectra 134 

Gases,  spectra  of 3 

Glycerol  solutions 134 

of  cobalt  salts 34 

of  erbium  chloride ...  63 
of  neodymium  salts.  .  78 
of  uranous  chloride . .  126 
of  uranyl  chloride 97 

Hydrochloric    acid,    effect   of,   on    the 
uranyl  acetate  bands 97 

Isomerism,  dynamic,  theory  of 12 


Liquids  and  solids,  spectra  of. 


Methods,  experimental,  used 19 

of  studying  emission  and  ab- 
sorption spectra 16 

Neodymium  nitrate  in  nitric  acid 79 

salts 69 

in  aqueous  solution, 
effects  of  temper- 
ature on  absorp- 
tion spectra  of. . .  72 

in  glycerol 78 

Nickel  acetate 44 

chloride 43 

in    water,    conductivity 

and  dissociation 45 

nitrate    in    water,    conductivity 

and  dissociation 45 

salts 43 

sulphate 44 

Nitrate  of  chromium 53 

of  cobalt 37 

of  copper 47 

of  praseodymium 66 

of  uranyl 86,  87 

Nitric  acid  solution  of  neodymium  ni- 
trate... ..   79 


Organic  absorption  spectra. . . 


10 


Phosphorescent  and  fluorescent  spectra 

of  uranyl  salts 116 

Plates,  description  of 147 

Potassium  chromate 25 

dichromate 26 

ferricyanide  in  water 28 

ferrocyanide  in  water 27 

salts,  absorption  spectra  of  .   23 

Praseodymium  chloride 65 

nitrate 66 

salts 65 

Previous  work,  review  of 31 


Results,  discussion  of 137 

Review  of  previous  work 31 

Solids  and  liquids,  spectra  of 6 

Solution,  solvate  theory  of 142 

Solvate  theory  of  solution 142 

Spectra  and  atomic  structure 9 

banded 7 

of  gases 3 

of  liquids  and  solids 6 

Spectrophotography   of  chemical   reac- 
tions    79 

Spectrophotography  of  chemical   reac- 
tions of  uranyl  salts 112 

Spectroscopic  investigations,  recent 1 

Spectrum  method  of  chemical  analysis . .     8 

problems,  complex 13 

Stark's  theory 13 

Sulphate  of  chromium 53 

of  cobalt 38 

of  nickel 44 

of  uranyl 88 

Sulphocyanate  of  cobalt 40 

Summary  of  results  with  cobalt  salts ...  42 
with        neodymium 
salts 83 

Temperature,  effect  of,  on  the  absorption 
spectra  of  aque- 
ous solutions  of 
neodymium 

salts 72 

on  erbium   chlo- 
ride in  water. .  63 
on  uranyl  acetate  112 
chloride  .  98 
nitrate  .  .  106 
sulphate .  108 

Theory  of  chromophores. 11 

of  dynamic  isomerism 12 

of  Stark 13 

Tysonite 61,  62 

Uranium  compounds,  absorption  spectra 

of 85 

salts 85 

alcoholic  solutions  of . ...  133 
Uranous  acetate,  absorption  spectrum 

of 131 

in  glycerol 132 

in  methyl  alcohol  and 

acetic  acid 131 

and    aluminium    chlorides    in 

water 123 

and  uranyl  acetates 130 

bands,  effect  of  the  presence  of 

acids  on 128 

bromide 130 

chloride,  effect  of  temperature 
on    the    absorption 

spectrum  of 132 

in  acetone  and  water  125 

in  glycerol 126 

and  water.  126 
in    hydrochloric    acid 
and  acetone 124 


INDEX. 


159 


Uranous  chloride  in  methyl  alcohol  and 

ether 128 

in   methyl   and   ethyl 

alcohols 125 

in  mixed  solvents 

124,  127,  134 

in  water 122 

and  ethyl  al- 
cohol  125 

to  which  acetic  acid  is 

added 130 

salts 121 

Uranyl  acetate,  anhydrous Ill 

bands,  effect  of   hydro- 
chloric acid  on 97 

in  methyl  alcohol Ill 

in  water 110 

conductivity  and 
temperature 
coefficients. . .  116 

temperature  effect 112 

and  uranous  acetates 130 

bands,  effect  of  dilution  on 102 

of  the  acetate 112 

bromide  in  water 108 

calcium,    aluminium    and    zinc 

chlorides  in  water 91 

chloride 88 

absorption  spectra  of . .  89 
and  calcium  chlorides  in 
methyl  alcohol. ......  94 

and  hydrochloric  acid  in 

water 91 

in  acetone 97 

and  water....   98 
in  aqueous  solutions.  ...  89 

in  ethyl  alcohol 96 

in  glycerol 97 

in  methyl  alcohol 93 

in   methyl   alcohol   and 
water 95 


Uranyl  chloride  in  mixtures  of    glycerol 

and  methyl  alcohol. . .  97 
in    water,    conductivity 
and  temperature  coef- 
ficients  115 

temperature  effect 98 

nitrate 86,  87 

absorption  spectra  of, 
under  different  condi- 
tions   99 

anhydrous,       absorption 

spectra  of 107 

crystals,  absorption  spec- 
tra of 101 

in  aqueous  solution 99 

in     ethyl     alcohol     and 

water 105 

in  methyl  alcohol 103 

in    methyl    alcohol    and 

water 103 

in  mixtures  of  glycerol, 
water,  acetone,  and 

ethyl  alcohol 106 

in  nitric  acid 102 

in  water,  conductivity 
and  temperature  coef- 
ficients  115 

temperature  effect 106 

salts  in  the  presence  of  free  acid.  134 
phosphorescent  and  fluor- 
escent spectra  of 116 

spectrophotography  of 
chemical   reactions   of..  112 

sulphate 88 

in  water,  conductivity 
and  temperature  co- 
efficients  115 

mixed  with  concentrat- 
ed sulphuric  acid. . . .  109 
temperature  effect 108 


PLATE  6 


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I.,  EUZABETH.    •     J. 


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PLATE  30 


CAMPBELL  ART  CO.. 


UIABITH.   I.   J. 


PLATE  35 


r  CO..    ELIZABETH. 


PLATE  36 


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PLATE  56 


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